Advanced maternal age increases the risk of very
preterm birth, irrespective of parity: a
population-based register study
U Waldenstr€om,a S Cnattingius,b L Vixner,c M Normand,e

a Division of Reproductive Health, Department of Women’s and Children’s Health, Karolinska Institutet, Stockholm, Sweden b Clinical

Epidemiology Unit, Department of Medicine Solna, Karolinska University Hospital, Stockholm, Sweden c School of Health and Social Studies,

Dalarna University, Falun, Sweden
d
Division of Paediatrics, Department of Clinical Science, Intervention and Technology, Karolinska

Institutet, Stockholm, Sweden e Department of Neonatal Medicine K78, Karolinska University Hospital, Stockholm, Sweden

Correspondence: Professor U Waldenstr€om, Division of Reproductive Health, Department of Women’s and Children’s Health, Karolinska

Institutet, Bastugatan 42, 118 25 Stockholm, Sweden. Email [email protected]

Accepted 20 August 2016. Published Online 21 October 2016.

Objective To investigate whether advanced maternal age is

associated with preterm birth, irrespective of parity.

Design Population-based registry study.

Setting Swedish Medical Birth Register.

Population First, second, and third live singleton births to

women aged 20 years or older in Sweden, from 1990 to 2011

(n = 2 009 068).

Methods Logistic regression analysis was used in each parity group

to estimate risks of very and moderately preterm births to women

at 20–24, 25–29, 30–34, 35–39, and 40 years or older, using 25–
29 years as the reference group. Odds ratios (ORs) were adjusted for

year of birth, education, country of birth, smoking, body mass index,

and history of preterm birth. Age-related risks of spontaneous and

medically indicated preterm births were also investigated.

Main outcome measures Very preterm (22–31 weeks of gestation)
and moderately preterm (32–36 weeks) births.

Results Risks of very preterm birth increased with maternal age,

irrespective of parity: adjusted ORs in first, second, and third

births ranged from 1.18 to 1.28 at 30–34 years, from 1.59 to 1.70
at 35–39 years, and from 1.97 to 2.40 at ≥40 years. In moderately
preterm births, age-related associations were weaker, but were

statistically significant from 35–39 years in all parity groups.
Advanced maternal age increased the risks of both spontaneous

and medically indicated preterm births.

Conclusions Advanced maternal age is associated with an

increased risk of preterm birth, irrespective of parity, especially

very preterm birth. Women aged 35 years and older, expecting

their first, second, or third births, should be regarded as a risk

group for very preterm birth.

Keywords Maternal age, parity, preterm birth.

Tweetable abstract Women aged 35 years and older should be

regarded as a risk group for very preterm birth, irrespective of

parity.

Linked article This article is commented on by KY Eichelberger,

p. 1245 in this issue. To view this mini commentary visit http://

dx.doi.org/10.1111/1471-0528.14464.

Please cite this paper as: Waldenstr€om U, Cnattingius S, Vixner L, Norman M. Advanced maternal age increases the risk of very preterm birth, irrespective

of parity: a population-based register study. BJOG 2017;124:1235–1244.

Introduction

So far, it has not been possible to prevent preterm birth,

mostly because the specific causes are complex and difficult

to establish in individual patients. Spontaneous preterm

birth is regarded as a syndrome initiated by multiple mech-

anisms, such as infection and inflammation, uteroplacental

ischaemia and haemorrhage, uterine overdistension, cervical

insufficiency, hormonal disorders, stress, or other immuno-

logically mediated processes.1

Targeting maternal risk factors for preterm birth in epi-

demiological studies might provide clues to the mecha-

nisms leading to preterm birth, and help to identify

women at risk.2 Low or advanced maternal ages have been

established as important risk factors for preterm birth,

along with socio-economic factors, smoking, low or high

body mass index (BMI), and an obstetric history of previ-

ous adverse events.
3–7

Whereas socio-economic confound-

ing may largely explain the increased risk of preterm birth

at young maternal age, this explanation seems less obvious

1235ª 2016 Royal College of Obstetricians and Gynaecologists

DOI: 10.1111/1471-0528.14368

www.bjog.org
General obstetrics

in relation to advanced maternal age.
8
Parity is another fac-

tor associated with preterm birth, with the highest rates

reported in nulliparous women and the lowest rates

reported in second births.5,6,9 The combined effect of

advanced maternal age and parity has been less explored,

as most studies have included nulliparous women

alone,10–15 or have treated parity as a covariate in the sta-

tistical analyses.
16–23

A limited number of studies compar-

ing nulliparous and parous women,
24,25

and studies

comparing first and second births,26,27 suggest that

advanced maternal age influences the risk of preterm birth

risk, regardless of parity. A review of studies from low- and

middle-income countries reported an increased risk of pre-

term birth in older women (≥35 years) expecting their
third birth or more, however.28

Considering maternal age and parity as two interrelated

risk factors that may affect pregnancy in different ways, it

is important to study their combined effect on the risk of

preterm birth. The principal aim of the present study was

to investigate associations between advanced maternal age

and risks of very preterm and moderately preterm birth in

first, second, and third childbirths, using a large popula-

tion-based cohort study. Subgroup analyses of spontaneous

and medically indicated preterm births were also

conducted.

Methods

The study was based on data from the Swedish Medical Birth

Register (MBR), which includes more than 98% of all births

in Sweden, and is validated annually against the National Pop-

ulation Register, using the mother’s and infant’s unique per-

sonal identification numbers.
29,30

Starting at the first antenatal

visit, information is prospectively collected during pregnancy

and delivery, using standardised records. We included live sin-

gleton births to women aged 20 years or older, recorded in

the MBR from 1990 to 2011. Consequently, the majority of

women contributed information about all of their births,

whereas some only provided information about their last birth

at the beginning of the observation period (1990), and others

only provided information about their first birth at the end of

the observation period (2011).

From 1990 to 2011, the total number of births in Swe-

den was 2 267 989. We excluded births to women younger

than 20 years (2.0%), births to women of parity 4 or more

(6.5%), multiple births (2.9%), stillbirths (0.3%), and preg-

nancies with missing data on gestation (0.1%) and unique

maternal identification number (0.1%), leaving 2 009 068

pregnancies in the final sample. Analyses stratified by spon-

taneous and medically indicated births were limited to the

period 2000–2011, when information about onset of labour
was most complete (99%), leaving 1 087 907 pregnancies

in the stratified analyses.

The outcome variables were very preterm birth

(22–31 weeks of gestation) and moderately preterm birth
(32–36 weeks of gestation), compared with pregnancies at
≥32 and ≥37 weeks of gestation, respectively. Specifying a
group of extremely preterm births (<28 weeks of gestation)
was not possible because of the insufficient power for anal-

yses by both maternal age and parity. The best available

estimate of gestational age was determined by a hierarchical

method based on expected date of parturition according to

ultrasound and last menstrual period.9 In Sweden, all

women are offered ultrasound pregnancy dating at

17 weeks or earlier, and more than 95% of women accept

this offer.31 Medically indicated births were defined as

either starting with the induction of labour or a caesarean

section before the onset of labour.

The independent variable was maternal age when giving

birth to the first, second, and third infant. In each parity

group, the maternal age range of 25–29 years was used as
the reference group, and compared with maternal ages of

20–24, 30–34, 35–39, and 40 years or older. The rationale
for the choice of reference group was the assumption that

25–29 years was an age range when outcomes would be
optimal,5,32 considering the U-shaped association between

maternal age and rates of preterm birth. The maternal age

range of 25–29 years was also the interval with the largest
number of live singleton births during the 21-year study

period (Table 1).

The principal analyses were adjusted for possible con-

founding factors, including year of birth, education,33,34

country of birth,3,33 smoking,15,33 BMI,15,33 and, in parous

women, history of preterm birth (<37 weeks of gesta-
tion).

35,36
Information about smoking (dichotomised as

daily smoking versus non-daily smoking), and maternal

height and weight were recorded at the first antenatal visit

(commonly at 8–12 weeks of gestation). BMI was calcu-
lated (weight/height2) and categorised according to the

World Health Organization as: underweight (BMI

<18.5 kg/m2), normal weight (BMI = 18.5–24.9 kg/m2),
overweight (BMI = 25.0–29.9 kg/m2), and obese (BMI
≥30.0 kg/m2). The Swedish Register of Total Population
provided information about the mother’s country of birth

(dichotomised as Nordic country, i.e. Sweden, Norway,

Finland, Denmark, and Iceland, versus not Nordic coun-

try). Level of education (low, elementary school or less;

medium, high school; high, college or university) was

obtained by linking to the Swedish Education Register. His-

tory of preterm birth was based on information about ges-

tational age at previous delivery recorded in the data set.

Additional analyses also included potentially mediating

factors occurring in the pathway between the independent

(maternal age when having a first, second, and third child)

and dependent (preterm birth) variables, such as gesta-

tional diabetes, pre-eclampsia, and small for gestational age

1236 ª 2016 Royal College of Obstetricians and Gynaecologists

Waldenstr€om et al.

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A
.

1237ª 2016 Royal College of Obstetricians and Gynaecologists

Risk of preterm birth by maternal age and parity

Table 2. Variables analysed, and their relationship with rates of very preterm (22–31 weeks of gestation) and moderately preterm (32–36 weeks
of gestation) live births (preterm birth)

Variables All pregnancies Very PTB Moderately PTB

n = 2 009 068 % n = 13 220* % n = 83 802** %

Materna age (years)

20–24 343 560 17.1 2306 0.7 15 991 4.7

25–29 710 196 35.3 4131 0.6 29 051 4.1

30–34 646 736 32.2 4082 0.6 25 049 3.9

35–39 264 222 13.2 2166 0.8 11 411 4.4

40 and older 44 354 2.2 535 1.2 2300 5.2

Parity

First birth 903 497 45.0 7560 0.8 46 734 5.2

Second birth 793 091 39.5 3856 0.5 26 043 3.3

Third birth 312 480 15.6 1804 0.6 11 025 3.5

Time

1990–1999 921 161 45.9 5961 0.7 38 688 4.2

2000–2011 1 087 907 54.1 7259 0.7 45 114 4.2

Education

Elementary school or less 219 117 11.2 1832 0.8 10 364 4.8

High school 962 883 49.1 6408 0.7 41 492 4.3

College or university 778 523 39.7 4555 0.6 29 711 3.8

Country of birth

Not Nordic 298 003 14.8 2364 0.8 12 543 4.2

Nordic 1 711 065 85.2 10 856 0.6 71 259 4.2

BMI (kg/m2)

Low: <18.5 41 383 2.7 279 0.7 2250 5.5

Normal weight: 18.5–24.9 993 000 64.3 5232 0.5 38 368 3.9

Overweight: 25–29.9 362 945 23.5 2264 0.6 14 722 4.1

Obese: ≥30 146 966 9.5 1349 0.9 7093 4.9

Smoking in early pregnancy

Yes 233 766 12.3 2029 0.9 11 611 5.0

No 1 669 868 87.7 9254 0.6 65 660 4.0

Pregestational hypertension

Yes 11 052 0.6 383 3.5 1085 10.2

No 1 998 016 99.4 12 837 0.6 82 717 4.2

Preeclampsia

Yes 56 943 2.8 2986 5.2 9922 18.4

No 1 952 125 97.2 10 234 0.5 73 880 3.8

Pregestational diabetes

Yes 12 180 0.6 231 1.9 1965 16.4

No 1 996 888 99.4 12 989 0.7 81 837 4.1

Gestational diabetes

Yes 16 993 0.8 148 0.9 1346 8.0

No 1 992 075 99.2 13 072 0.7 82 456 4.2

Intrauterine growth restriction (SGA)

Yes 46 988 2.3 3265 6.9 6689 15.3

No 1 956 773 97.7 9633 0.5 76 530 3.9

PTB in first pregnancy*** Second births: n = 793 091 n = 3856*** n = 26 043***

Yes 36 689 5.8 876 2.4 5195 14.5

No 590 702 94.2 1996 0.3 14 621 2.5

PTB in second pregnancy**** Third births: n = 312 480 n = 1804**** n = 11 025****

Yes 11 015 4.9 332 3.0 1645 15.4

No 213 615 95.1 888 0.4 6058 2.8

Denominators: *2 009 068; **1 995 848 (very PTB excluded); ***second births only—very PTB, 793 091; moderately PTB, 789 235 (very PTB
excluded); ****third births only—very PTB, 312 480; moderately PTB, 310 676 (very PTB excluded).

1238 ª 2016 Royal College of Obstetricians and Gynaecologists

Waldenstr€om et al.

(SGA). Also, pregestational hypertension and diabetes were

included in these analyses, as these diseases are associated

with age.

Data on maternal diseases were retrieved from the MBR:

pregestational diabetes [insulin dependent or non-insulin

dependent; International Classification of Diseases, ninth

revision (ICD-9) codes 250 and 648A; ICD-10 codes E10–
E14 and O240–O243], gestational diabetes (ICD-9 code
648W; ICD-10 code O244), pregestational hypertension

(self-reported by check box at first antenatal visit, or by

ICD-9 codes 401–405, 642C, and 642H, or by ICD-10
codes 110–115, O10, and O11) and pre-eclampsia (includ-
ing eclampsia; ICD-9 codes 642E–642G; ICD-10 codes O14
and O15). The registry also provided information about

SGA infants, defined as a birthweight of more than two

standard deviations below the mean for gestational age,

according to a sex-specific Swedish reference curve for

normal fetal growth.37

Pregnancies of nulliparous women (first births) and

pregnancies of women classed as para 1 (second births)

and para 2 (second births) were analysed separately (like

three cross-sectional studies). Rates of preterm birth were

calculated for each age group. The associations between

maternal age and each outcome were investigated by logis-

tic regression analyses. First, we adjusted for year of birth

(model 1). In the principal analyses (model 2), we also

adjusted for mother’s education, country of birth, smoking

habits, BMI, and in parous women also for preterm birth

in the previous pregnancy. Finally, we also adjusted for

potentially mediating factors (model 3).

The levels of missing data were low for the total sam-

ple (maternal age, 0%; parity, 0%; education, 2.4%;

country of birth, 0%; smoking, 5.2%; maternal diagnoses,

0%; and SGA, 0.3%), except regarding BMI (23.1%) and

history of previous preterm birth (20.9% in second births

and 28.1% in third births). Missing data on BMI (mater-

nal weight and height) was substantially explained by the

time-point when this information was included in the

Medical Birth Register. Missing data on history of previ-

ous preterm first and second births, respectively, were

related to how the study sample was defined, with infor-

mation missing in parous women who had their previous

birth prior to the onset of data collection in 1990. We

estimated the missing values in these three variables to

be nearly at random, and thus meeting the criteria for

multiple imputation.38 Imputations were conducted in

SPSS 22 (IBM Corporation, Armonk, NY, USA), in three

separate data sets, including first, second, and third

births, respectively. The SPSS ‘Automatic’ imputation

method was used (type of imputation model: logistic

regression), and 25 imputations were performed. The

imputed variable in the data set of first births was BMI,

the imputed variables in the data set of second births

were BMI and history of preterm birth in the first birth,

and the imputed variables in the data set of third births

were BMI and history of preterm birth in the second

birth. The variables used in the imputation procedure

included the outcome variables (very preterm birth, mod-

erately preterm birth, spontaneous and indicated very

preterm birth and moderately PTM respectively), and all

the independent variables listed in Table 2 (except par-

ity). All findings presented in Figure 1 and Table 1 are

based on the pooled estimates. Findings based on com-

plete case analyses are briefly described. (Principal find-

ings based on both original and computed data are

presented in Table S1).

0

1

2

3

4

5

6

7

20–24 25–29 30–34 35–39 ≥40 20–24 25–29 30–34 35–39 ≥40

Pe
rc

en
t

Maternal age

1st births 2nd births 3rd births

Moderately PTBVery PTB

Figure 1. Rates of very and moderately preterm birth (PTB) by maternal age in first, second, and third births (values presented in Table 1). Total

samples: first births—very preterm, 903 497; moderately preterm, 895 937; second births—very preterm, 793 091; moderately preterm, 789 235;

third births—very preterm, 312 480; moderately preterm, 310 676.

1239ª 2016 Royal College of Obstetricians and Gynaecologists

Risk of preterm birth by maternal age and parity

Results

In pregnant women aged 20 years or older who had their

first, second, or third birth, the overall rates of live single-

ton preterm birth were stable during the entire 21 years of

observation: 0.7% delivered very preterm and 4.2% deliv-

ered moderately preterm.

Table 1 presents the variables analysed in the study, and

the rates of very and moderately preterm birth in relation to

these variables. Figure 1 illustrates that rates of very and

moderately preterm birth increased after 30–34 years, and
were most prevalent in first births. In parous women, the dis-

tribution of moderately preterm birth was U-shaped, with

increased rates in both the youngest and older age groups.

The risk of very preterm birth, expressed as adjusted

odds ratio, increased from maternal age 30–34 years in
approximately the same way in first, second, and third

births, and ranged from 1.18 to 1.28 at 30–34 years, from

1.59 to 1.70 at 35–39 years, and from 1.97 to 2.40 at
≥40 years (Table 2, model 2). Having a third child at a
young age (20–24 years) was also associated with an
increased risk compared with the reference group.

The risk of moderately preterm birth increased by mater-

nal age from age 35–39 years, and ranged from 1.16 to
1.41 at 35–39 years, and from 1.22 to 1.74 at ≥40 years
(Table 2, model 2). The age-related risks of moderately

preterm birth were consistently lower than the correspond-

ing risks of very preterm birth. As with very preterm birth,

the youngest women expecting their third birth had a

slightly higher risk than the reference group.

By including age-related pregnancy complications,

pregestational hypertension, and diabetes, the age-related

risk of very preterm birth was reduced in all parity groups,

but remained statistically significant, except in the youngest

age groups and in women who had their second and third

0
0.5

1
1.5

2
2.5

3
3.5

4

A
dj

us
te

d
O

R
(9

5%
C

I)

Maternal age

Very preterm 1st births

0
0.5

1
1.5

2
2.5

3
3.5

4

A
dj

us
te

d
O

R
(9

5%
C

I)

Maternal age

Moderately preterm 1st births

0
0.5

1
1.5

2
2.5

3
3.5

4

A
dj

us
te

d
O

R
(9

5%
C

I)

Maternal age

Spontaneous Indicated

Very preterm 2nd births

0
0.5

1
1.5

2
2.5

3
3.5

4

A
dj

us
te

d
O

R
(9

5%
C

I)

Maternal age

Moderately preterm 2nd births

0
0.5

1
1.5

2
2.5

3
3.5

4

A
dj

us
te

d
O

R
(9

5%
C

I)

Maternal age

Very preterm
3rd births

0
0.5

1
1.5

2
2.5

3
3.5

4

A
dj

us
te

d
O

R
(9

5%
C

I)

Maternal age

Moderately preterm 3rd births

Spontaneous Indicated Spontaneous Indicated

Spontaneous Indicated

Spontaneous Indicated Spontaneous Indicated

Figure 2. Spontaneous and medically indicated births by maternal age in first, second, and third births, 2000–2011. Adjusted odds ratio (OR) with
95% confidence interval (95% CI). Reference 1: maternal age 25–29 years. Analyses adjusted for education, country of birth, smoking, BMI, and, in
parous women, history of preterm birth in the previous pregnancy.

1240 ª 2016 Royal College of Obstetricians and Gynaecologists

Waldenstr€om et al.

birth at 30–34 years. A similar pattern was found in mod-
erately preterm births (Table 2, model 3).

Figure 2 illustrates the adjusted odds ratios of sponta-

neous and medically indicated preterm birth by parity and

maternal age, based on data from the second half of the

observation period. The risk of both spontaneous and med-

ically indicated very preterm births increased from mater-

nal age 30–34 years or 35–39 years. Also, the risk of
medically indicated moderately preterm birth increased by

maternal age, whereas the associations with spontaneous

moderately preterm birth were weak, and were non-existent

in first births. Similarly to the previous analyses (Table 2),

women who had a third birth a young age (20–24 years)
deviated from this pattern by being at higher risk than the

reference group. When including the potentially mediating

factors (the same factors listed in Table 2, model 3), the

age-related adjusted odds ratios for spontaneous preterm

birth remained essentially unchanged, whereas risks of

medically indicated preterm birth were substantially

reduced (data not shown). Still, women aged 35 years and

older were at increased risk of very preterm indicated first

births, and moderately preterm indicated first and second

births.

In first births, the presented findings based on imputed

data (BMI) were nearly identical as those based on com-

plete case analyses. In second and third births, the odds

ratios based on imputed data (BMI and history of preterm

birth) were marginally higher (Table S1 presents models 2

and 3 with both original and imputed results).

Discussion

Main findings
We found that the risk of very preterm birth increased with

maternal age, irrespective of parity. In moderately preterm

births, the age-related associations were weaker, but still

obvious from age 35–39 years and older. Advancing mater-
nal age increased the risks of both spontaneous and medi-

cally indicated preterm birth; the exception was

spontaneous moderately preterm birth in a woman’s first

delivery.

Strengths and limitations
The strengths of this study include the high quality of data

in the Swedish Medical Birth Register, with few missing

cases (<2%), and the possibility to take important con-
founding factors into account. Including the history of pre-

term birth in the analyses of second and third births was

particularly important considering that heredity is a strong

predictor of preterm birth.39 Still, residual confounding

may be a problem: in the case of cervical surgery or previ-

ous termination of pregnancy, for example. Another limita-

tion was the high proportions of missing values for BMI

and history of preterm birth, which justified multiple

imputation; however, the findings presented in this analysis

were basically the same as those obtained by complete case

analysis, and none of the conclusions were altered.

Interpretation
The stronger association between advanced maternal age

and risk of very preterm birth, compared with moderately

preterm birth, is supported by other studies.
7,40,41

Our

results support the suggestion that advanced maternal age

is a risk factor for preterm birth over the full gestational

age range, but with more pronounced effects at the lower

end.7 This interpretation is also supported by findings that

the rate of miscarriage increases with advancing maternal

age.42 The physiological pathways may differ between very

and moderately preterm birth, however, with greater simi-

larities between miscarriage and very preterm birth than

between miscarriage and moderately preterm birth.

Intrauterine infection is the only pathological process for

which a causal link with preterm birth has been estab-

lished.1,43 We had no information on rates of chorioam-

nionitis, but pregnancy at age ≥35 years has been
associated with a decreased risk for chorioamnionitis than

pregnancy at age 25–29 years.44 If anything, this could only
have introduced conservative bias into our estimates of

age-related effects.

Advanced maternal age may contribute to the placental

and myometrial vascular lesions associated with preterm

birth.45,46 In indicated births, associations with advanced

maternal age were largely mediated by pre-eclampsia and

SGA (which both increased with maternal age within each

parity group), and these conditions are associated with vas-

cular disorders and decreased utero-placental blood flow.
47

Hormonal disorders, such as progesterone deficiency, is

another potential pathway. Progesterone is important for

pregnancy maintenance,48 and levels decline with maternal

age. Women diagnosed with luteal-phase deficiency, char-

acterised by progesterone deficiency, had lower rates of pre-

term birth if they were treated with progesterone than a

group without such treatment.
49

Our finding that advanced

maternal age carries a higher risk for very preterm birth

lends support to the hormone-deficiency hypothesis.

Emotional stress could also be at play in the causal path-

way. We found higher rates of potential stressors in the

very preterm group, such as migrant background, smoking,

overweight, and history of preterm birth. Stress may also

have contributed to the higher risk of preterm birth

observed in women who had their third birth at a young

age (20–24 years). Compared with the reference group
(25–29 years), these women were more exposed to factors
related to social vulnerability, including low level of educa-

tion, non-Nordic country of birth, and smoking. Although

these factors were adjusted for in the statistical analyses,

1241ª 2016 Royal College of Obstetricians and Gynaecologists

Risk of preterm birth by maternal age and parity

young mothers may also have been more exposed to

unmeasured factors related to psychosocial vulnerability,

and life stress and anxiety have been associated with short-

ened gestation.50

The independent effect of parity on pregnancy outcomes

is less explored. There is some evidence suggesting that the

haemodynamic adaptation occuring during the first preg-

nancy may permanently modify the uterine arteries, con-

tributing to decreased vascular resistance and facilitated

uteroplacental blood flow in the next pregnancy.51,52 This

may explain the higher birthweights with increasing parity,

particularly of the second born,53 and the lack of association

between advanced maternal age and stillbirth in second preg-

nancies.54 Such an explanation could be relevant for the

lower rates of preterm second and third births, as the SGA

rate (mediating factor) was higher in first births (3.3%),

compared with second and third births (1.5 and 1.6%,

respectively). Nevertheless, this interpretation does not shed

light on our principal finding that parity did not modify the

effect of advanced maternal age on risk of preterm birth.

The division into spontaneous and medically indicated

births may be less pertinent for the understanding of how

advanced maternal age acts on the risk of delivering pre-

term; however, from a clinical point of view it is of interest

to show that advanced maternal age increased the risks of

both spontaneous and indicated very preterm births.

From a public health perspective, advanced maternal age

together with smoking and being overweight probably rep-

resent the most important modifiable risk factors for preg-

nancy complications such as very preterm birth.15,55

Parturients aged 35 years or older in the Nordic countries

increased from 5% in 1975 to around 20% in 2012,
56

and

a similar development has taken place in many other coun-

tries. This rapid change in the reproductive epidemiological

landscape has contributed to a significant number of very

preterm births. Despite a predicted overall increase in very

preterm births during the study period (women aged

≥35 years increased from 14% in 1990–1999 to 22% in
2000–2011, and women who were overweight increased
from 29 to 36%, respectively), we found a stable rate of

preterm births over the study period. This indicates that

the adverse effects of advanced maternal age and over-

weight were outweighed by changes in other risk factors:

for instance, the reduction of smoking in early pregnancy

(from 16 to 6%), and possibly also the increase of women

with college or university education (from 34 to 53%).

Although preterm infant survival is high nowadays, and

has also increased for those born extremely preterm,
57

very

preterm infants is one of the most resource-demanding in-

hospital patient groups, and the final outcome is not

always full health.58,59 To challenge the continuing rapid

increase in maternal age, increased professional and

political knowledge as well as parental and public informa-

tion on the increased risk for preterm birth is warranted.

Conclusion

Our study suggests that advanced maternal age is an inde-

pendent risk factor for very preterm birth, irrespective of

parity. Although the absolute risk for very preterm birth

decreased in multiparas, possibly suggesting a benefit from

physiological adaptations during the first pregnancy, the age-

related increase in risk remained unchanged. The size of the

effect suggests that the risk of very preterm birth is of clinical

importance for pregnant women aged 35 years or older. In

moderately preterm births, advanced maternal age was only

associated with a modestly increased risk of medically indi-

cated preterm births. These findings help to move research

on age-related pathways for preterm birth forwards, and may

help in designing and testing effective interventions.

Disclosure of interests
None declared. Completed disclosure of interests form

available to view online as supporting information.

Contribution to authorship
UW (guarantor of the article) initiated the study, con-

ducted the analyses, and wrote the first draft of the paper.

SC contributed to the concept and design of the study,

interpretation of the data, and revision of the article

regarding important intellectual content. LV participated in

the analyses and interpretation of the data, and in the revi-

sion of the article. MN contributed to the concept and

design of the study, interpretation of the data, and revision

of the article regarding important intellectual content. All

four authors approved the final version of the article for

publication, and agreed to be accountable for all aspects of

the work in ensuring that questions related to accuracy or

integrity of any part of the work are appropriately investi-

gated and resolved.

Details of ethics approval
The study was approved by the Regional Ethics Review Board

in Stockholm, 15 May 2013 (reg. no. 2013/731-31/1).

Funding
No extra external funding was sought for this study. It was

conducted within the frame of our academic positions.

Acknowledgements
The authors thank all of the women, midwives, and obste-

tricians who provided data for this study by completing the

antenatal, intrapartum, and postpartum records on which

the Swedish National Medical Birth Register is based.

1242 ª 2016 Royal College of Obstetricians and Gynaecologists

Waldenstr€om et al.

Supporting Information

Additional Supporting Information may be found in the

online version of this article:

Table S1. Risk of very and moderately preterm birth by

maternal age in first, second, and third births, presented

with original data (complete case analyses) and imputed

data &

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Health Care for Women International, 28:534–555, 2007
Copyright © Taylor & Francis Group, LLC
ISSN: 0739-9332 print / 1096-4665 online
DOI: 10.1080/07399330701334356

First Mothering Over 35 Years: Questioning the
Association of Maternal Age

and Pregnancy Risk

M. CAROLAN
School of Nursing and Midwifery, Victoria University, Melbourne, Australia

S. NELSON
School of Nursing, University of Toronto, Toronto, Canada

Women having a first baby at 35+ years are commonly considered
to be “at risk” for pregnancy complications. This understanding
appears to be based primarily on age, and curerntly many healthy
women are included in this category. There is clear evidence to
suggest that, for these women, being considered “at risk” is anxiety
provoking.

In this Australian qualitative study of first mothering over
35 years, we found four risk-related themes, “realizing I was at
risk,” “hoping for reassurance,” “dealing with uncertainty,” and
“getting through it/negotiating risk.” We concluded that successful
adjustment to motherhood related principally to participants
negotiating risk and also to the infant growing and becoming
more responsive. Attitudes of health professionals were found to
contribute to rather than ameliorate participant dilemmas.

Understanding how healthy women over 35 years engage with
and negotiate notions of risk may assist health professionals in the
provision of more meaningful maternal support for this growing
group of women.

BACKGROUND

In the past four decades, there have been many changes to childbearing
trends in the advanced industrial world. Those changes include fewer

Received 1 September 2005; accepted 26 August 2006.
Address correspondence to Dr. Mary Carolan, School of Nursing and Midwifery,

Victoria University, St. Albans Campus, P.O.Box 14428, Melbourne 8001, Australia. E-mail:
[email protected]

534

Questioning the Risk 535

children, born closer together, to older mothers. This “graying” of maternity
gives rise to many concerns and dilemmas, not the least of which is the asso-
ciation of maternal age and pregnancy risk among healthy mature women.
First-time mothers over 35 years are often labeled as “elderly primigravidae”
and as “at risk,” which is an issue of concern to a wide range of health
professionals and to a growing group of parturient women and their families.

Historically, the term “Elderly primigravida” was first coined in the 1950s
to describe women of 35 years and above embarking on their first pregnancy
(International Council of Obstetricians, 1958; as cited by Barkan & Bracken,
1987, p. 101 Waters & Wager, 1950). At that time, obstetric outcomes for “el-
derly” mothers were considered to be significantly less favorable than those
for younger women. Mature childbearing of this era tended to be an indicator
of socioeconomic disadvantage (Neumann & Graf, 2003; Wildschut, 1999),
and very often included mothers of many children who had commenced
childbearing several years earlier. First mothering over 35 years was a rela-
tively unusual event and typically was related to late marriages or infertility
(Harker & Thorpe, 1992). Now, however, in the twenty-first century, maternal
age greater than 35 is an increasing trend in the developed world (Australian
Bureau of Statistics [ABS], 2000, 2003; Australian Institute of Health and
Welfare [AIHW], 2000; National Statistics U.K., 2001; U.S. Center for Disease
Control and Prevention, 2001), and a significant percentage of this group
are first-time mothers. This pattern relates to changing social trends and
value shifts, including increasing female participation in higher education and
the workforce (Berkowitz, Shovron, Lapinski, & Berkowitz, 1993; Berryman,
Thorpe, & Windridge, 1999; Cunningham & Leveno, 1995; Hewlett, 2002a,
2002b; Ozer, 1995) and feminist ideology of the last four decades (Welles-
Nystrom, 1997), which has changed the possible trajectory of women’s lives.
Currently, for women actively engaged in a career, postponement of first
birth is usual, and for many, this juncture at 35+ may represent the first
opportunity for pause in a woman’s working life (Hewlett, 2002b).

The resulting cohort of childbearing women, though not homogeneous,
tends to be composed of well-educated women (Berryman et al., 1999;
Stark, 1997), who participate in highly paid employment (Berkowitz et al.,
1993; Berryman et al., 1999; Ozer 1995). As such, these women are likely
to be financially secure (Cunningham & Leveno, 1995), to pursue healthy
lifestyle choices (Berryman et al., 1999), to eat a balanced diet and to
abstain from smoking (Berryman et al., 1999; Najman, Lanyon, Andersen,
Williams, Bor, & O’Callaghan, 1998). Higher maternal education is also
commonly associated with increased health awareness and greater use of
health care facilities (Morrison, Najman, Williams, Keeping, & Anderson,
1989; Raum, Arabin, Schlaud, Walter, & Schwartz, 2001; Richman, Miller, &
LeVine, 1992). Nonetheless, despite their well-educated and well resourced
status, contemporary women appear to experience later first mothering as
problematic. Particular difficulties are said to include heightened anxiety

536 M. Carolan and S. Nelson

(Nicholson, 1998; Windridge & Berryman, 1999) and an increased incidence
of postnatal depression.1 Greater attendance at mother and baby units is
noted (Fisher, Feekery, Amir, & Sneddon, 2002), and it seems likely that
perceptions of mature first mothering, as risky, may impact negatively on
the experiences of these women.

Literature Review

THE CONSTRUCTION OF RISK FOR “OLDER” PREGNANCY

The notion of risk as applied to maternity over 35 years, particularly
primiparity, appears to be composed of two separate strands. The first is
concerned with medical risk, as related to an aging reproductive system, and
an aging body, which is considered less able to withstand the physiological
challenges of pregnancy. The second includes a social discourse of risk,
which embodies notions of the “right time to have a baby,” and also includes
suggestions of responsible risk management such as availing of prenatal
testing.

Within the medical literature, “older” mothers (over 35 years) and their
infants are considered to be at increased risk of multiple complications
(Ataullaha & Freeman-Wang, 2005) including high blood pressure (Barton
et al., 1997; Heffner, 2004; Kullmer, Zygmunt, Munstedt, & Lang, 2000),
preeclampsia (Heffner, 2004; Sibai et al., 1997; Tan & Tan, 1994), gestational
diabetes (Amarin & Akasheh, 2001; Bobrowski & Bottoms, 1995; Dildy
et al., 1996), maternal mortality (Ataullaha & Freeman-Wang, 2005; Freeman-
Wang & Belski, 2002), chromosomal abnormality (Heffner, 2004; Hollier,
Leveno, Kelly, McIntire, & Cunningham, 2000), prematurity (Ataullaha &
Freeman-Wang, 2005; Scholz, Haas, & Petru, 1999), low-birth-weight infants
(Bonellie, 2001; Cnattingius, Forman, Berendes, & Isotalo, 1992; Scholz
et al., 1999), and unexplained stillbirth (Anderson, Wohlfahrt, Christens,
Olsen, & Melbye, 2000; Fretts, 2001; Heffner, 2004; Jacobsson, Ladfors, &
Milsom, 2004). Throughout, there is a suggestion that the over 35 mother
and her infant fare less well than younger mothers, although the actual
statistics relating to infant morbidity do not significantly differ between the
groups. This theme of greater risk without actual increase in infant morbidity
is repeated in several studies, such as those by Pollock (1996); Prysak, Lorenz,
and Kisly (1995); Spellacy, Miller, and Winegar (1986); and Smit, Scherjon,
and Treffers (1997). Similarly, British psychologists, Windridge and Berryman
(1999), who conducted a broad based-comparative study among pregnant
women of all ages, discovered that “professionals were more likely to place
women over 35 years than those aged 20 to 29 years in a ‘high-risk’ category,

1 Maternal depression following birth commonly described as postnatal depression in Australia and
as postpartum depression in the United States.

Questioning the Risk 537

but medical records of labor and delivery revealed few maternal age effects”
(p. 16).

What is not clear from the literature is the extent to which age-associated
risk relates to preexisting maternal compromise, for example, chronic
hypertension or to lifestyle influences, such as smoking, maternal weight,
and general health. It seems likely that today’s healthy mature mothers
may not attract the same degree of risk as did mature maternity of earlier
decades. Some researchers, such as Mansfield and McCool (1989), suggest
that researchers have failed to allow for important contextual differences
in the childbearing experiences of younger and older women. This, they
contend, can account for a considerable portion of differential results,
“mistakenly ascribed to reproductive age” (p. 395). In a related theme,
Hanson (2003) suggests that negative views of female aging lead to the
conclusion that “older” maternity is filled with risk, and also that this belief
persists in the absence of corroborating evidence.

In addition to medical discourses of “older” maternity as fraught with
physical compromise, social discourses construct later first mothering as
both problematic and risky. These discourses are underpinned by notions
of socially “appropriate” time to childbear and according to Daniels and
Weingarten every generation has an “implicit consensus about the right
time” to become a parent (1982, p. 13). That “right” time is contingent on
prevalent social mores and in contemporary Australia is at approximately
30 years, similar to the statistical average age of childbearing (ABS, 2003).
Consequently, women over 35 years, and especially those over 40 years
having a first baby, may feel “out of time” with their peers (Dobrzykowski &
Stern, 2003; Neurgarten & Datan, 1973; Rossi, 1980) and also may feel that
in postponing pregnancy that they have contributed to physiological risk.
Notions of age-associated pregnancy risk are ubiquitous, and Lupton’s (1999)
work on “pregnancy risk” is drawn upon here to explicate this association.
Although Lupton’s work centers on pregnancy in general, and does not
make age-related comparisons, it seems likely that this view of pregnancy
at 35+, as especially risky, is an extension of the discourse of risk that
surrounds all pregnant women. Indeed, the notion of risk in pregnancy seems
to have grown considerably in recent years and may relate to advances in
risk-related knowledge and technologies within prenatal care. Greater public
awareness may also contribute. Whatever the origin, Lupton considers that
“the [pregnant] woman is surrounded by and constructed through a plethora
of expert and lay advice” (1999, p. 89). This advice is directed at how she
should conduct her life to best facilitate the development of her precious
fetus. Prevalent discourses suggest that she is responsible for her baby’s
health, and should she ignore medical advice, then she has only herself
to blame if things go badly (Lupton, 1999). Lupton further suggests that
the pregnant woman is positioned in a “web of surveillance” that requires
constant effort on her part, such as “seeking out knowledge about risks to

538 M. Carolan and S. Nelson

her fetus, acting on that knowledge” (p. 89). Women are generally compliant
and “choose” prenatal testing because they too want to maximize their
chances of having a perfect baby. Discourses of risky mature mothering
are common in lay literature and, indeed, one need only look at women’s
magazines and newspapers to understand that “older maternity is difficult
and risky.” Beaulieu and Lippman (1995) present a useful case in point.
These researchers surveyed the contents of 10 major women’s magazines
for stories about “mature” pregnancy and associated risks and found three
commonly articulated themes: a “need” for women to be fully informed of
the facts and risks of being pregnant when older; a further need to find out
the physical state of the fetus (through medical testing); and a suggestion
that the pregnant woman can best meet these needs by “choosing prenatal
diagnosis” (p. 59). Throughout most of this literature, concepts of risk are
interwoven with suggestions of responsible bahavior, aimed at “ensuring”
the health of the fetus.

Methods

SAMPLE

The study reported here involved a longitudinal, qualitative study conducted
at a major maternity hospital in metropolitan Melbourne, Australia, and
recruitment is described in detail elsewhere (Carolan, 2005a). In brief,
primigravid women aged 35+ were recruited purposively on the basis of
age and primiparity. The following inclusion criteria were employed:

Ĺ First-time mothers,
Ĺ aged 35 years or mature at time of booking,
Ĺ uncomplicated pregnancy,
Ĺ no major underlying medical complication,
Ĺ english speaking.

In all 22 women were interviewed. Following recruitment it was apparent
that participants fell by self-selection into two groups, women who
considered themselves career women (n = 16) and those who did not
(n = 6). In addition to being well-educated (tertiary degree/diploma), career
women tended to be self-proclaimed “high achievers” and “perfectionists.”
They included a doctor, a journalist, accountants, lawyers, businesswomen,
an academic, computer specialists, a project manager, a teacher, and a
registered nurse. For the most part, these women described approaching
childbearing as a well-delineated “plan” and most had reached a certain
level of career achievement prior to choosing to conceive. Almost all had
postponed childbearing in pursuit of other goals/career plans. For some,
the motivation for having a baby was related to feeling that “time was

Questioning the Risk 539

running out” or that now was the “right time.” For two mothers, increasing
dissatisfaction with work provided the trigger. A total of 16 mothers fit this
category, 7 of whom had required some degree of intervention to conceive.

The remaining 6 women did not mention career as an identifying
characteristic, and this group of women was less likely to have electively
delayed childbearing. Most spoke of having wanted a baby for quite some
time but parturition plans had been thwarted by lack of a partner, divorce,
reluctance in a partner, or fertility difficulties. Of the 6 women who fit this
category, 4 had completed high school and the remaining 2 had left school
during year 11. Their occupations included hairdresser, receptionist, waitress,
exotic dancer, secretary, and clerk. These women tended to describe being
“really ready for a baby/aching for one” and described their pregnancy as a
“dream come true.”

DATA COLLECTION AND RATIONALE

Data from a larger qualitative study investigating the transition to moth-
erhood experiences of first-time mothers over 35 years (Carolan, 2005a)
provided the material used in this secondary analysis. The prime intent
of that study was to examine the broad experience of first maternity
for “older” childbearing women, and participants described a temporally
ordered progression through well-defined junctures at 1–4 weeks, 1–4
months, 4–6 months, and 6–8 months. Although specific questions about
perceptions of risk were not asked, it nonetheless became clear that the
notion of risk was pervasive and underpinned the women’s accounts.
Indeed the data seemed to “tell two stories.” The first story was the
sequential transition to motherhood (reported in an earlier paper, Carolan,
2005b) and the second story seemed to relate to the negotiation of
risk.

Although risk was reviewed in the earlier article as a background
characteristic, it actually went much deeper than this and over time I (first
author) became concerned that this notion of risk, particularly as it applied
to maternal age, had not been given due attention. Later conversations
with midwifery colleagues and obstetricians confirmed my fears. The notion
of risk, as allied to “older” maternity, was everywhere, and this premise
was firmly held by many health professionals. I revisited the data and
found that many participants had indeed been consumed with angst,
which they related to “the risks they were facing,” and at this point I
decided to reanalyze the data from a new lens, specifically seeking out
notions of risk. I also looked specifically at the question, “What might have
helped?” asked in the final interview, to see if participants were retrospec-
tively providing answers on ways to provide more meaningful maternal
support.

540 M. Carolan and S. Nelson

DATA ANALYSIS

Data were systematically analyzed using thematic content analysis and
followed the following steps. I (first author) read and reread the data and
sought out statements and terms that seemed related to risk. Examples
included, “The odds seemed stacked against us,” “I thought I was fine, til
I found out about all the risks,” and “I realized I was in a bad category.”
These terms and fragments were highlighted and moved together within
individual accounts. Later when rereading gave me a broader understanding
of individuals’ experience of risk, these highlighted areas were matched up
with similar ideas from other women’s accounts and then within the body of
data. At each stage, data were reduced to exclude words that detracted from
key ideas. In this way, analysis progressed through increasingly higher levels
of abstraction, until only themes and related fragments remained. Similar
methods have been abundantly described in the literature surrounding
qualitative research, for example, Bowling (2002), Clifford (1997), Downe-
Wamboldt (1992), Graneheim and Lundman (2003), Holsti (1969), Morgan
(1993), Patton (2002), and Robson (2002).

Through repeated discussion with colleagues in clinical practice and
reflection, and reading and rereading of the reduced data, it eventually
became clear to me that participants journeyed through distinct stages in
relation to risk. Those stages were highlighted in identifying colors and
separated out of the main body of data. Final data analysis involved the
amalgamation of 4 separate themes: “realizing I was at risk,” “hoping for
reassurance,” “dealing with uncertainty,” and “getting through it/negotiating
risk.”

Findings

REALIZING I WAS AT RISK

Here, many participants described their prepregnancy health as above
average, which is consistent with other studies of primiparae over 35 years
(Berryman et al., 1999; Ventura, 1989). On interacting with the health system,
however, these women often learned that, despite prepregnancy health, they
were now regarded as being “at risk” related to their age. There is some
suggestion within the literature that this labeling of “high risk” and “elderly
primigravida” contributes to perceptions of heightened fetal vulnerability
(Berryman et al., 1999; Payne, 2002), and a similar association is noted
here. Participants describe their surprise at realizing they were considered to
be at risk, despite their understanding of good health. Elizabeth (40 years)
explains:

Before I had the baby I was very fit. I worked out at the gym and
went to yoga and swimming regularly. I thought I would be pretty okay

Questioning the Risk 541

during pregnancy, especially since no one in my family had ever had any
problems [having babies]. Then I went to see the doctor and he painted
a very different picture. He said because of my age and all that, that he
would need to see me more often and I would have to go to Clayton
[tertiary facility] in case I needed an emergency delivery. He said I was
more at risk. I walked out of there thinking, “Oh my God, the baby could
die, I could die.”

Abigail (39), too, picked up on age-associated risk and felt her
pregnancy was disadvantaged by her age:

I worried, too, about my age, I worried ’cause they said there was a
greater chance that things could go wrong with the baby. I worried; I
counted his fingers and toes. I think partly my age makes a difference
in that I thought, “If something happens to our baby, you know, what
chance have we got?”

And Carol (43) felt concerned that her pregnancy was particularly subject
to loss, because of age-related physiological changes:

So far as my age is concerned, I’m in the top end of IVF. . . . I worried that
I didn’t have enough of the right hormones to keep him. . . . it seemed
like the odds were stacked against us. . . . All the reading was done out
in percentages [of having a healthy term infant] and they just kept going
down and down [related to advancing age]. . . . “God,” I thought, “I’m in
a really bad category. . . .”

HOPING FOR REASSURANCE

Most women in this study were cared for in tertiary-level care, which seemed
unrelated to “medical risk status.” This “choice” appeared to have been driven
by both the women and care providers. Increased surveillance was common
and, in turn, precipitated a snowball effect of testing and retesting. The
women, well-educated, articulate, and Internet literate, for their part, often
insisted on additional ultrasonic scans and genetic testing as reassurance for
their perceivably vulnerable pregnancy. Although most women described
being keen to know if anything was “wrong with the baby,” repeated testing
seemed to fuel rather than alleviate anxiety. For example, Jane describes
anxiously moving along from one test to the next, hoping for some reassuring
news:

So at all these scans, I had one at 6 weeks, 12 weeks, 18 weeks, another
one a week after that, and 33 weeks, and I would go hoping that they
would say, “Everything’s fine, you don’t have to come back anymore. . . .”
But I tended to look at the scans and, like I’ve no idea what I’m looking

542 M. Carolan and S. Nelson

at, and I’d think, “Oh, that doesn’t look good!” I didn’t ask questions, I
tended to just look at it, “What’s that flapping?” It can’t be right, there’s
something wrong with that!”

The flapping Jane describes is the fetal heartbeat, though such was her
fear when she attended her various scans and tests that she never asked
for an explanation. Meanwhile, Elizabeth was so concerned about having an
abnormal infant that she did everything in her power to prevent this from
happening:

We decided we would make a final determination when we found out if
anything was the matter with it, so we had some additional tests because
we thought, there was no way. . . . I didn’t think I would want to bring
a child into the world with all those problems. We’ve got a couple of
friends who’ve given birth to children and at birth something happened
to them. . . .

And Petra explains how each new test brought a new level of worry:

And you know, all those tests, I was sure they would find something
wrong. We had the first scan and they found that the baby’s kidney was
swollen, so we had to have more scans to check that was okay. Then
they found a cyst on his head. That really worried me as we were advised
to have the amnio, so we did that. It just seemed to go on and on . . .
like one thing just led to another, and in the end it was all for nothing
[nothing was wrong].

Jane describes the agony lurching from one test to another, hoping for
good news: “I went through this sort of . . . being healthy, waiting for the
next scan, praying he’s alright, but it does put . . . that urgency on you. . . .”

When the sought for reassurance did not eventuate, several participants
described how they dealt with the uncertainty of “not knowing.”

DEALING WITH UNCERTAINTY

Here, most women addressed concerns about risk in one or both of two
clearly defined ways: seeking out more information or suspending their
emotional investment in the pregnancy. Some leaned particularly toward
accessing information in a bid to be as fully informed and prepared as
possible, and several went to impressive lengths to understand “what they
were facing.” Some had read as many as 12 pregnancy and medical guides.
A few women had read several more. This tendency was seen exclusively
among career-orientated participants and, for these women, this was a
normal work strategy. Rachel presents a case in point and discusses how
at ultrasound that it was discovered that her baby had two vessels in the

Questioning the Risk 543

cord (rather than the more usual three). She describes her frustration in
accessing information about this variance and, retrospectively, wishes she
had not known:

I felt that every time they told about something that I had, like the one
artery [in the cord] that was a different branch of research that I couldn’t
get from them . . . I felt it would’ve been better for me not to know there
was one artery, not to know. . . . Because of my PhD I am someone who
likes to research. . . . I had to do all these searches to get any information
and it was only in American books that I found reference to it. . . .

Jane muses on how she approached pregnancy, rationalizing that she
could not do it any differently:

I suppose with work and all that. . . . like we’ve come to a certain point
where we know a lot more than we would have 20 years ago, and we
want to know, the risks and all that. . . . I don’t know if I could approach
it any other way. . . . If my doctor didn’t give me enough information, I
would’ve got it somewhere else. . . .

For many, keeping some distance from the pregnancy helped them to
deal with the uncertainty of “not knowing.” For example, Carolyn describes
not wanting to get too close to her twin babies when she was not sure what
might eventuate:

The reason I don’t know what my babies are, whether they’re boys or
girls is because I didn’t want to know. . . . For me it was if I knew they
were two boys or two girls or boy and girl, I would start planning their
life. And what happens if I didn’t make it to week 18? For me it was
to prevent . . . not to get too close to them. . . . I can do that, just put
things aside. . . . I had to. . . . At week 15 they told me I was AFP positive
and I had gone to my ultrasound on Thursday and then he phoned, and
whenever he phoned, it’s like, “Oh no, what now,. . .” and he said, “Now
don’t worry, 95% of the women with alpha protein don’t have it (neural
tubal defect), so you have 5% risk. . . .” It’s like a lottery. . . .

Jennifer worked at distracting herself from risk-related thoughts:

Well, that issue was worrying me, was she going to be okay? . . . It used
to get into my head and I would just get up and do things so I didn’t
have to think about it. . . . I’d watch a movie or I’d be doing things, I’d
be cleaning up in the kitchen, ironing. . . .

Elizabeth on the other hand, took a more proactive approach and
demanded a caesarean delivery:

544 M. Carolan and S. Nelson

So I walked into the doctor and I said to him, “When we have this baby, I
want to have a caesarean,” and he said, “What for?” and I said I wanted to
counteract all these difficulties. I know that that’d be a real life sentence
to have a child like that and that your life is, you know, the years have
ticked on and you’ve now lost 10 more years of your life and it’s going
to be taking up the next 20 years with a seriously difficult situation.

Even when the baby was born fit and well, many mothers continued
to be overly concerned about the infant’s health and possible imminent
demise. Most continued to read extensively; however, reading did little to
allay their anxiety. Several displayed a limited understanding of normal
neonatal behavior and a seeming inability to distinguish normal behavior
from more significant concerns. This situation seems to be a consequence of
understanding the baby to be at “high risk.” Professional attitudes were also
identified by participants as adding to their dilemmas.

PROFESSIONAL ATTITUDES: ADDING TO THE DILEMMA

Although it should be pointed out that most women were happy with the
care they received in hospital, several considered that health professionals
were insensitive and dismissive of their concerns. Jane explains:

The gynecologist was far too dismissive for my liking! I would often
leave there feeling like I didn’t get my questions answered, and felt like
I’d been deprived a bit,. . .Like questions about what would happen if
I had to have a caesarean, he dismissed me. . . . Everything I read or
discussed with anyone else pointed that way, and if I mentioned it to
him, he’d just say we’ll see later on, your health’s okay, don’t worry! And
he would brush me off and I found that really frustrating.

This study also found that participants often would pretend they were
managing well in the early postpartum period, rather than ask for assistance,
particularly if the “vibes” from the midwife or carer were unfavorable. Many
worried about asking “dumb questions.” Rachel had this to say:

Suddenly this baby’s there and I think there’s an expectation, a lot of the
nursing staff. . . . because you’re older, [think] that you instinctively know
what to do, but I don’t think you do. . . . It makes you sometimes feel a
little bit inferior because you don’t know what to do . . . just a few looks
or comments or whatever, you think, “Should I have known that? Was
that a dumb sort of question?”

Others describe a difficulty in losing face and particularly valued
respectful engagement. These women spoke of disliking to be patronized,
spoken down to, or “told off” by nursing staff. Sally explains:

Questioning the Risk 545

I was just so fed up with the constant changing [advice]. That was
probably the biggest problem, that week in the hospital and I’m the
sort of person that I don’t like to be criticized and at this stage of your
[sic] life, I’m 45, for goodness sake, I don’t like to be talked down to, and
a lot of them [nurses] did, and I didn’t like that!

“GETTING THROUGH IT” NEGOTIATING RISK

Here, being at risk was experienced by mothers as something of a “crisis”
related principally to perceptions of infant vulnerability and concerns of
infant demise. This situation was mostly resolved by approx 4–6 months
postpartum, however, and participants spoke of suddenly realizing that the
infant was “just a baby,” rather than the enormous responsibility she or
he had been until this point. At this stage, most participants had relaxed
their approach to mothering and, interestingly, the infant seemed to bring
about this change and help lessen the mother’s anxiety. Several women also
had gained sufficient perspective to rationalize the risk for their particular
situation. Abigail explains:

You know the first few months I used to bring her to the doctors probably
every week, and I used to worry so much about SIDS and about her
dying. . . . You know, it was risk, risk, risk and then nothing [no follow
up]. You don’t sort of realize how nervous you’ve become. . . . I suppose
for me the big turnaround came when she started smiling and, you know,
she was glad to see me. . . . It made me realize sort of that she was a
person . . . and that there was really no reason why she would just get
sick. . . . I tried to remind myself that my mother raised all of us without
hardly ever going to the doctor. . . . I mean, I still worry, but not anything
like as much as at first. . . .

And Kerri found that as her baby grew she began to realize it was less
fragile: “All of a sudden you just realize it’s just a baby, I’m not treating it
like a China doll anymore. . . .”

Jane had this to say:

when I look back now, I don’t know how I got through it. . . . I was a
nervous wreck before the baby was born. . . . It took a long while for me
to forget that so many things could go wrong. . . . I remember thinking
when he was born, “Phew, that worked, now I’ve just got to keep him
[prevent him from dying]!” I went through this terrible worry about SIDS.
I would check him a hundred times between feeds . . . and even things
went through my mind, like what on earth if I die? I didn’t expect to go
through the sort of anxiety I went through. . . . I talked to my sister a
lot, ’cause we’ve always been really close, and that helped me a lot. She
had her children when she was very young, and she sort of could see

546 M. Carolan and S. Nelson

that what I was doing was because I was older and because of the IVF
and thinking I’d never get through it [get through the pregnancy without
miscarrying]. . . . I think with that support and Kevin, I guess growing and
becoming what I perceived as stronger and not feeling as wobbly [better
neck control], like you’ve got to be really careful in the beginning.

What Might Help?

During the final interview, women in this study were asked what might
have helped during their transition to early motherhood. When revisiting
the data for this article, specific suggestions related to negotiating risk
were sought, and, overwhelmingly, mothers had suggested that having
some positive information about mature mothers would have helped. These
women described receiving information outlining age-related pregnancy risk,
fetal disorders, and declining odds of successful fertility treatment. Most
suggested that they perhaps were not so much empowered by having this
information as terrified by the burden it imposed. Abigail explains:

I think that that the overemphasis on the problems that older women
have is very destructive, and I really want to emphasize that point. It’s
destructive to her capacity to just roll into the role [cope]. I already feel
far more competent than a lot of women that are 10 years younger than
me, but I was so afraid about whether this baby was going to be okay.

Having some positive information on mature mothering may have
helped mothers gain a little perspective. Jane explains:

. . . like you telling me you knew someone who’s 48 having her first
child, when you said that to me I thought, “Wow, isn’t that terrific, isn’t
that brilliant?” It’s, like, amazing, because I wasn’t at any point when I
was building up towards having Kevin. . . . That’d probably help a lot
of people in our position, because there isn’t a lot of information, you
know, on the view that over 40 or 45 you really still had hope. . . .

And Jennifer had this to say:

Well, that’s the other thing, with an older Mum, I think it would be lovely
to have people who are older Mums that can actually talk, understand
you, that have actually been [through it]. . . a lot of people don’t really
understand. . . . I mean, you understand it because of the study and that
sort of thing and hearing other people, if you’re not, if you’ve had your
kids when you were younger and see someone else, it is very hard to . . .
you sort of have to put your best foot forward so they don’t think you’re
hopeless. . . .

Questioning the Risk 547

Many women also felt they would have benefited from having some
easily accessible brief written information on on basic care such as how to
settle an infant to sleep, and how to recognize an unwell infant might have
proved helpful and allayed concern. Anthea and Jennifer explain:

I think they should discuss the safety, as in what happens if your baby
chokes, or coughs, how do you cope? Or simple things like when they’re
sick, don’t panic! It could be this, it could be this, how to recognize a
sick baby. . . . It would help if you had some basic information to refer
to.

We couldn’t get him to sleep, we didn’t know what to do, all this sort
of stuff. . . . You come home with nothing [from the hospital]. Well, the
babies don’t know what to do anyway, you don’t even have anything
written out to [refer to] that gave me an idea of how long they should
be sleeping, all that sort of thing and when, how many feeds. You really
have to work all that out yourself. . . . You don’t know in the beginning
that it’s not going to die of crying. Looking back now, I didn’t realize
really how fragile I was. . . . If someone had just given us something
[information] about how to get him to sleep. . . .

In retrospect, many recognized that initial worries related more to
heightened anxiety during pregnancy than to any untoward event. Notwith-
standing an initial anxious period, however, the women of this study were
found to be proactive seekers of services and advice, and reported a
successful though somewhat delayed transition to motherhood.

RESOURCEFUL AND PROACTIVE

Despite common understandings of mature primiparae as superanxious
and prone to high levels of postnatal depression, participants here did
not demonstrate high levels of postnatal maladjustment. Indeed, of the
22 mothers in this study, only one suffered from a minor degree of
postnatal depression [PND], which is significantly less than the estimated
national incidence of approximately 10%–20% of all new mothers (Bewley,
1999; Green, 1998). Although many participants identified an early need
for additional professional and social support, most were confident and
proactive in seeking assistance to meet their needs. Additionally, after
an initial adjustment period, the women’s organizational skills and work
experiences seemed to equip them well to deal with childcare dilemmas
and decisionmaking. Gayle and Sally explain:

I’d always had to organize things at work, so the skills that were there
actually came to the fore a bit with her. . . .

548 M. Carolan and S. Nelson

I would just go to plan B. I’ve been a project manager for many years,
and we always come up with problems and hiccups and you get over
them, so, fortunately, that’s my background. So, if there’s a hiccup, that’s
okay, so what are my other options. My options are this, so let’s see if
we can do that.

By 6–8 months most were overwhelmingly positive about their expe-
riences and variously described mothering as the best thing they had ever
done. Annie seems to sum up the mood:

I only have to look at her. It’s the best thing I’ve ever done in my life, it’s
the most frightening thing I’ve ever done. . . . You know when people
say I’ve done a lot of silly things, and I’ve done a lot of wrong things,
but this is the best thing I’ve ever done in my life.

DISCUSSION

Many parallels are to be found among the experiences of this study’s
participants and those of all new mothers, particularly in regard to new
maternity as a time of disruption, anxiety, and chaos (Antonucci & Mikus,
1988; Barclay, Everitt, Rogan, Schmied, & Wyllie, 1997; Pridham & Chang,
1992). Some new information is also reported here, however, and it relates
principally to the high levels of concern voiced by participants who all
had healthy full-term pregnancies. A delayed though ultimately successful
negotiation of risk is reported by these women, despite common perceptions
of maladjustment. Some confounding factors, such as tensions between
participants and health care professionals, also are discussed.

Overall, it is clear that the application of an “at-risk” label alters the
experience of maternity for women aged 35+. For most, this means having
restrictions placed on care options, such as being denied the option of care
at a low-risk facility. Almost invariably, it means that the woman is exposed
to increased pregnancy surveillance (Berryman et al., 1999; Windridge &
Berryman, 1996), including additional screening tests (Muggli & Halliday,
2003; Bell, Campbell, Graham, Penney, Ryan, & Hall, 2001). In addition
to extra screening, Bell and colleagues (2001) found that “older” first-time
mothers were more likely to have an antenatal admission, more than
two scans, amniocentesis, caesarean section, assisted delivery, induction,
and augmentation than were younger women. At the same time, higher
levels of intervention among older women were not explained by obstetric
complications. Greater intervention in turn appears to affect higher rates
of maternal morbidity (Albers, Lydon-Rochelle, & Krulewitch, 1995; Ecker,
Chen, Cohen, Riley, & Lieberman, 2001; Freeman-Wang & Belski, 2002;
Scholz et al., 1999) and so the care received by this group of women

Questioning the Risk 549

may become a self-fulfilling prophecy of greater intervention leading to
poorer outcomes. Although it is not immediately apparent what drives this
pattern, many explanations are posited. For example, Freeman-Wang and
Beski suggest that “anxiety in both the mature mother and the obstetrician
may be responsible for a greater degree of medical intervention” (2002, p.
41). Meanwhile, Albers and colleagues (1995) found an association between
maternal social advantage and increased caesarean section rates. Others have
suggested that decreasing maternal fertility and fertility treatment together
impact on caesarean rate for primiparae older than 40 years (Scheiner,
Shoham-Vardi, Hershkovitz, Katz, & Mazor, 2001), while still others suggest
that medical fears spur the physician to greater caution with this group
(Freeman-Wang & Belski, 2002).

Although it is not entirely clear that this group of women is truly at
greater risk physiologically, it is clear that a small increase in risk appraisal
may result in an inordinate emotional response in the mother (Baillie, Smith,
Hewison, & Mason, 2000; Getz & Kirkengen, 2003; Watson, Hall, Langford,
& Marteau, 2002). For example, Getz and Kirkengen (2003), who discussed
differences in risk perception between physicians and women, suggested that
“to the clinician, risk retains the character of a population-based number, but
to the individual pregnant woman, the population base is one, herself, and
‘one in a hundred’ means that she can be the one” (p. 2051). This situation
of being considered at risk and being referred for additional tests caused
participants in this study considerable angst, and many described entering
maternity as “nervous wrecks.” Many dealt with anxiety by seeking out
more information, and women discussed reading avidly, conducting Internet
searches, and seeking information from doctor’s surgeries and hospitals.
Nonetheless, this access to information did little to reassure them and
instead seemed to heighten anxieties. Moreover, the largely medical-type
information favored by well-educated women in this study seemed to
alert them to myriad additional possible complications in the fetus. Lesser
educated women here, although also concerned, seemed to embrace a less
expansive range of worries and tended to access information on a “need
to know” basis. Similar findings of greater information searching among
well-educated and well-resourced women are reported in the literature,
for example, Deutsch, Brooks-Gunn, Fleming, Ruble, and Stangor (1988);
Gottesman (1992); Mercer (1986); and Viau, Padula, and Eddy (2002).

Some participants considered that professional attitudes and misun-
derstandings contributed to their dilemmas, and several discussed mid-
wives/nurses and doctors as dismissive of their concerns, particularly minor
worries and attention to detail such as, “How long should I burp my baby
for?” These attitudes can perhaps be explained by busy workloads and also
by the fact that the facility in which the participants gave birth also cared for
seriously ill pregnant women, some of whom had life-threatening conditions.
In this major hospital, the minor concerns and time-consuming questions

550 M. Carolan and S. Nelson

of the mature primipara may have been given little priority by midwives
and other health professionals when compared with other “real” concerns.
Additionally, extensive worries and “knowing too much” caused a certain
percentage of participants to challenge health professionals, many of whom
did not know the latest research on every obscure event. This degree of
knowledge acquisition is frequently understood by health professionals as
problematic and inappropriate, and as contributing to the difficulties mature
mothers face (Dobrzykowski, 1998). Indeed, health professionals often find
well-informed mature primiparae to be a challenging and demanding group
to care for, and, in this study, a sense of antagonism arose between health
professionals and participants. Career women particularly were extremely
knowledgeable about all sorts of eventualities and seemed to then distrust
health professionals who were unable to answer their questions. Together
these factors made for a tumultuous initial postpartum period. A resolution
of sorts ultimately was brought about by the mothers themselves and related
to the women “working through” the risk rather than having their needs met
by health care regimes.

CONCLUSION

This research is a beginning in identifying the special needs of mature
first-time mothers, particularly career-orientated postponers. These women
represent a new social group and, as such, do not fit within contemporary
Western notions of maternity. Nonetheless, they are a growing cohort,
particularly in affluent countries, and it is important that health professionals
learn as much as possible about the needs and experiences of this group of
mothers in order to better support their transition to motherhood. There is
some evidence to suggest that current health care regimes do not cater well to
their needs and also that professional preconceptions and misunderstandings
affect their experiences of maternity. Close attention to the experiences
described and recommendations made by participants here may shed some
light on the unique experiences and challenges of first-time mothering over
35 years. New understandings gained here may thus inform future nursing
and medical care for this group of women.

Finally, notions of risk impact negatively on mature mothers in terms
of concern and additional surveillance. At the same time, it is not clear just
how advanced maternal age alone contributes to risk in a healthy cohort. It
is therefore important that current perceptions of maternal age, as a predictor
of pregnancy risk, are challenged. Further broad-based studies are needed
to establish the true level of risk for healthy mature childbearing women.

Questioning the Risk 551

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ORIGINAL ARTICLE Infertility

‘Inconvenient biology:’ advantages and
disadvantages of first-time parenting
after age 40 using in vitro fertilization
K. Mac Dougall1, Y. Beyene1, and R.D. Nachtigall1,2,*
1Institute for Health and Aging, University of California, San Francisco, 3333 California Street, Suite 340, San Francisco, CA 94114, USA
2Department of Obstetrics, Gynecology and Reproductive Sciences, University of California, San Francisco, CA, USA

*Correspondence address. Tel: +1-415-661-3913; E-mail: [email protected]

Submitted on August 19, 2011; resubmitted on December 19, 2011; accepted on January 5, 2012

background: As ages at first birth have steadily risen in the industrial west over the last several decades, the phenomenon of ‘delayed
childbearing’ has come under research scrutiny by demographers, medical specialists and social scientists. In this study, we specifically explore
the perceived advantages and disadvantages of postponed conception as well as participants’ retrospective opinions on the ‘optimal age’ for
parenting.

methods: To this end, we examined a cohort purposely chosen to epitomize delayed childbearing, i.e. men and women who used IVF to
conceive at the very end of their reproductive capability. In-depth qualitative interviews were conducted between 2009 and 2011 with 46
couples and 15 individual self-selected US women and men who had used IVF to conceive their first child when the woman was aged 40 or
older at the time of delivery. Although the demographics of this cohort were consistent with others who use IVF in the USA, their median
income was 3 – 4 times higher than that of the average US family, which may bias their largely positive parenting experiences.

results: Most women and men believed that childbearing later in life resulted in advantages for themselves and their families. These
included having established careers with financial security and career-time flexibility, enhanced emotional preparedness, committed co-par-
enting relationships and a positive overall family experience. The main disadvantage was the unexpected difficulty in conceiving that culmi-
nated in the use of IVF and resulted in a smaller family than desired, although many expressed feeling ‘lucky’ to have children at all. Other
disadvantages were lack of energy for parenting, less available lifetime to spend with children and anticipated stigma as older parents.

conclusions: These disadvantages appear to have influenced conception and parenting experiences so that in hindsight the majority of
participants identified the optimal age for first-time parenting as 5 – 10 years earlier than they had conceived. This age range was imagined to
maximize the financial and emotional advantages of later parenting while minimizing the impact of age-related infertility, diminished energy,
anticipated health issues and the social stigma of appearing too old to parent.

Key words: delayed childbearing / late parenting / age-related infertility / IVF / advantages/disadvantages

Introduction
‘If it weren’t for the inconvenient biology, I really think 35 to 45 is a
great time to have kids. That may not be true for everybody’.
Female Participant.

As ages at first birth have steadily risen in the industrial west over
the last several decades (Billari et al., 2007; Matthews and Hamilton,
2009), the phenomenon of ‘delayed childbearing’ has come under
research scrutiny by demographers, medical specialists and social
scientists (Temmerman et al., 2004; Collins et al., 2005; Hammarberg
and Clarke, 2005; Benzies et al., 2006; Bray et al., 2006; Browning,
2007; Reddy et al., 2007; Buckles, 2008; Usta and Nassar, 2008;
Alviggi et al., 2009; Malizia et al., 2009; Simpson, 2009; Billari et al.,

2010; Boivin et al., 2010; Bretherick et al., 2010; Balasch and Gratacós,
2011; Beets, 2011). Risks of delayed parenting have also been enum-
erated in medically oriented studies that document infertility, poor
birth outcomes and potential developmental problems in offspring
(Bray et al., 2006; Reddy et al., 2007; Usta and Nassar, 2008;
Alviggi et al., 2009; Malizia et al., 2009; Balasch and Gratacós,
2011). Other studies have focused on the social risks of delayed child-
bearing primarily for those who remained infertile and/or childless as a
result of age-related infertility (Fisher et al., 2010; van Balen and
Trimbos-Kemper, 1993; Gunilla et al., 2005; Wirtberg et al., 2007;
Johansson et al., 2009; Volgsten et al., 2010).

A few studies have addressed the psychological well-being of older
parents and offspring (Finley, 1998; Mirowsky and Ross, 2002;

& The Author 2012. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology. All rights reserved.
For Permissions, please email: [email protected]

Human Reproduction, Vol.27, No.4 pp. 1058 – 1065, 2012

Advanced Access publication on February 14, 2012 doi:10.1093/humrep/des007

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Bornstein et al., 2006; Spence, 2008; Boivin et al., 2009) and have
identified some positive and negative aspects of the late parenting
experiences of women who conceived with or without the use of
their own eggs and/or assisted reproductive technologies (Carolan,
2005; Friese et al., 2006; Shelton and Johnson, 2006; Browning,
2007). However, no research has focused exclusively on the experi-
ence of couples or single parents in which the woman had given
birth after the age of 40 using IVF. Examining a cohort purposely
chosen to epitomize delayed childbearing, i.e. men and women who
used IVF to conceive at the very end of their reproductive capability,
in this study, we specifically explore the perceived advantages and dis-
advantages of postponed conception as well as participants’ retro-
spective opinions about the ‘optimal age’ for parenting.

Methods
This qualitative exploratory research was funded by the National Institute
of Child Health and Human Development and was approved by the insti-
tutional review board at the University of California, San Francisco. The
sponsor was not involved in study design; the collection, analysis and inter-
pretation of data,or the writing and submission of this article. Respondents
were recruited through two IVF centers in Northern California. Practi-
tioners sent letters to 400 former female patients who had used IVF to
conceive their first child, and were age 40 or older at the time of delivery.
There was no age requirement for participating partners. These criteria
were selected to identify couples and individuals who had delayed
childbearing.

Between 2009 and 2011, the research team interviewed 46 couples and
15 individuals (15% of families approached), a cohort adequate for
in-depth, qualitative data analysis (Langness and Frank, 1981; Morse and
Field, 1995; Hammersley and Atkinson, 2007). All participants reviewed
and signed informed consent documents prior to being interviewed.
Initial couple interviews were followed by individual interviews with each
partner �3 months later to collect data on how couples jointly perceived
IVF and parenting and to allow individuals to discuss differences without
their partner present. Only one couple was unavailable for the individual
second interview. If one but not both members of a couple agreed to
be interviewed, those respondents were interviewed individually. Single
participants were also included in the study. The semi-structured inter-
views were 1 – 2 h long. Demographic data were collected and interviews
were recorded and transcribed verbatim.

Preliminary core categories were generated from meanings in the data,
and a process of code development took place (Strauss and Corbin, 1990;
Luborsky, 1994; Mays and Pope, 2000). Successive phases of trial coding
were conducted until pairs of coders reached a high level of agreement
(Mays and Pope, 1995; Pope et al., 2000). The data were then coded
using Atlas.ti, a qualitative data analysis program (Muhr, 1993 – 2011).
This article contains an analysis of the code ‘Advantages/Disadvantages’
defined as discussion of ‘advantages and disadvantages of becoming
parents later in life’ and the code ‘Optimal’ defined as ‘discussion of
optimal age to have children, optimal life course, reflections on things
that could have been different or better in retrospect’. The data include
responses to the interview questions ‘What are the advantages and disad-
vantages of being parents at this time in your life?’ and ‘Is there an optimal
age range in which to have children?’ posed to all participants, as well as
any ad hoc discussion of these topics. All of the data coded ‘Advan-
tages/Disadvantages’ were analyzed together and then separately in the
larger context of the interview. Subsequently, secondary themes were
detailed.

Results
The median age at the birth of their first child was 42 years for women
and 43 years for men. The majority of participants were Caucasian,
employed, married, had a post-graduate education, identified as a
member of a religious group and reported median family incomes of
$150 000 – $199 000.

Most families had one child via IVF (median age 3.5 years, range
,1 – 10). In seven families, male partners had children from previous
relationships (median age 23 years, range 9 – 36). Approximately 75%
used their own gametes for conception via IVF, 15% used donor
sperm and 10% used donor eggs or both to conceive one or more
children. The demographic description of the cohort is detailed in
Table I.

Advantages of parenting later in life
A majority of women and men in the study believed that childbearing
later in life resulted in advantages for themselves and their families.
The most frequently cited advantages are illustrated in Table II and
included enhanced emotional preparedness, greater financial security
and work-time flexibility, committed co-parenting relationships and a
positive overall family experience. As one woman summarized:
‘Except for the actually getting pregnant part, for me, it’s mostly
been just a lot of advantages’.

Emotional preparedness, ‘No Regrets’
Almost three-quarters of the women and over half the men cited their
perception that they had enhanced emotional preparedness for par-
enting which was of benefit to both their children and themselves.
Frequently cited attributes of emotional preparedness were ‘maturity’,
‘patience’ and ‘self-awareness’; as one man summarized: “I know that
I’m way more self-aware than I was 20 years ago. I feel like I’m in a
better position to communicate better with my child and help them
more in life and I understand how to be a supportive, encouraging
parent”. Some felt that their experiences in life had made them
more resilient and capable; as this woman put it: ‘I think I’m probably
a calmer mother than I might have been years ago . . . I just have more
confidence in myself than I did in my 20′s, so I don’t get fazed by as
much as I might have when I was younger’. Some spoke about
having a sense of maturity, which contributed to their enjoyment of
and enhanced focus on parenting: ‘You know, you just don’t sweat
the small stuff. I think partly because I’m 40 now and because I
have a lot of the trappings of success, or have had them and they
haven’t always made me happy, I think I’m more interested in just
my son and me enjoying his childhood together’.

For others, their earlier life experiences before having children were
a source of self-enrichment and satisfaction: ‘I did a lot of stuff I
wanted to do before I had kids. I lived abroad, I traveled a lot, I
have an interesting career, so I felt very self-actualized’. This was
seen as preventing feelings of regret about the time-consuming obliga-
tions of parenthood; as one woman put it: ‘I had 21 years from being
out of high school to having kids and I feel like I had a great time; I did a
lot of stuff. So I don’t feel like I’m missing out . . . that is something that
I appreciate having my kids older’. Another woman elaborated:
‘We’ve done a lot of selfish things, and so I don’t feel deprived
when I have to spend all day long with [my] son and clean up poop

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and spit-up and that kind of thing. To me, it’s just a welcome gift as
opposed to any kind of burden, and I think that comes with just the
experience we’ve had and the fact that we’re so old, we’ve had a
chance to do the other stuff’.

Career associated advantages
Having an established career with financial security or the flexibility to
reduce their working hours, work at home or schedule their work
days to better suit their personal and family needs was cited by
over one-third of men and nearly half of women. Those in established
careers appreciated that they no longer had to ‘prove themselves’ at
their jobs by working extra hours or engaging in lengthy travel. One
woman reflected on the greater latitude and opportunities she experi-
enced by having children later in life: ‘If I had gotten pregnant when I
was 26, I would have been in business school. The trajectory of what
windows would have been open to me would have changed. That’s no
longer true. I have a reputation. I have a history. I have a little bit of
political capital to spend. So, if I need to take three months off and
have a kid, I can do it’. Parents also discussed how having advanced
in their careers improved their confidence and sense of achievement,
and made it easier for them to re-orient their priorities to spend time
and energy with their families while maintaining a connection to their
professions; for example: ‘I’m at the perfect point for having kids . . . .I

…………………………………………………………………………….

Table II Advantages of first-time parenting over age 40
using IVF.

Women
(n 5 65), (%)

Men (n 5 42),
(%)

Emotional preparedness 72 57

Career/work flexibility 43 31

Financial security 31 36

Perception of strong Partner/
family Relationships

22 12

…………………………………………………………………………….

Table I Study demographics.

# %

Total families 61 100

Couples 46 75

Individual women whose partners did not
participate

9 15

Single women 6 10

Total number of study participants 107 100

Women 65 61

Men 42 39

Age

Median age of women at the birth of their first
child

42 (40 – 46)

Median age of men at the birth of their first child
via IVF

43 (35 – 67)

Marital status

Heterosexual marriages/partnerships 51 83

Same sex female marriages 4 7

Single women 6 10

Men who had previous families 7 17

Children

Median number of children per family 1 (1 – 3)

Median age of first child 3.5 (.1 – 10)

Number of families with one child after IVF 40 66

Number of families with two children after IVF 18 29

Number of families with three children after IVF 3 5

Conception methods

IVF 46 75

IVF with donor sperm 9 15

IVF with donor eggs 6 10

Median months trying to conceive prior to IVF 6 (0 – 60)

Average total cycles of IVF 2 (1 – 6)

Ethnicitya,b

Caucasian 96 83

African American 2 2

Pacific Islander 1 1

Asian 6 5

More than one race 1 1

Middle Eastern 5 4

Other 2 2

No ethnicity reported 3 3

Household incomeb

$0 – $99 999 5 9

$100 000 – $149 999 11 18

$150 000 – $199 999 17 28

$200 000 – $249 999 8 13

More than $250 000 19 31

Not reported 1 2

Employmenta,b

Women employed full-time 34 52

Continued

…………………………………………………………………………….

Table I Continued

# %

Women employed part-time 15 23

Women without paid work 16 25

Men employed full-time 41 80

Men employed part-time 8 16

Men without paid work 2 4

Educationa,b

High school 1 1

Some college 12 10

College 47 39

Post graduate 56 46

No education reported 6 5

aSome individual participants reported on behalf of spouses.
bSome participants did not report in some categories.

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had some time to get some experience and . . . can go back to work
easier than if I had [kids] right out of grad school’.

The secure financial resources that frequently accompanied a
successful career were specifically cited as an advantage by over a
third of men and almost as many women. Parents wanted to be
able to provide for their families without ‘struggling’, for example; ‘I
think it’s much better this way. I’m financially sound, stable . . . . I’m
not sitting there wondering how I’m gonna put the groceries on the
table or provide for my children’. Secure finances were also associated
with greater flexibility and options in parenting styles. For example, this
father said: ‘I got to the point where I’d done the career thing and I’d
made some money that I could invest, I mean we’re not set for life or
anything, but I felt like now was a point where . . . this would be a great
time for me to now be a parent because I could be at home, I could be
more involved and contribute more to the family’.

Seven male participants had older children from previous relation-
ships. A common theme among them was the increased time available
for parenting compared with their experience with the children they
had in their earlier relationships. They reported feeling more involved
in daily parenting tasks and enjoying being more active in parenting
than they had in the past. They attributed this change largely to
decreased time and/or energy that they had previously devoted to
career building and income generation. For example, this father
described: ‘. . . as an older parent . . . all the things that I see [my
son] do . . . I didn’t get to see with my other two children because I
was working in a job where it was necessary for me to be not only
dependable and reliable but to establish a reputation . . . now I get
to . . . be the kind of dad that I should have been before’.

Relationships and family life
Cited by over a fifth of women but only half as many men as an advan-
tage of later childbearing was the establishment of stable and
committed relationships with partners. These were perceived to be
beneficial for both men and women, and contributed to a positive
family environment for children. Almost all participants characterized
their partners or spouses as being involved and sharing parenting
tasks. For some participants, their own or their parents’ previous
unsuccessful relationships influenced their decisions about when and
with whom to have children. For example, as this woman explained:
‘I wouldn’t have done it differently because I really felt like I needed
to be at a certain place in my relationship. Maybe I feel bad that it
took so long for me to get to that place, but I have past history . . .
and I didn’t want to bring a child into that’. Many men and women
were surprised to be having so much fun parenting and felt that
having children later in life was keeping them young. For example,
this woman described: ‘I mean I can be a child through his eyes
again and experience things through his eyes that I wouldn’t do at
this age if I didn’t have him’. Some, such as this father, reported
that having children at this point in their lives kept them physically
fit: ‘He will keep us younger and involved and being active, hiking,
biking and so forth’. Women in the sample noted that being parents
became their defining social identity rather than their chronological
age. For example, parents of school-aged children often described
relationships with younger parents which had the positive affect of
keeping them more culturally current.

Disadvantages of parenting later in life
While a majority of participants framed parenting later as largely posi-
tive, a smaller percentage enumerated disadvantages. These disadvan-
tages are depicted in Table III and included infertility and the need to
utilize IVF in order to conceive, the lack of physical energy for parent-
ing, less lifetime in which to enjoy children, smaller family sizes and
concerns about being stigmatized as ‘older’ parents.

Difficult conception
For almost half the women but less than a third as many men, the
primary disadvantage of later parenting was their difficulty conceiving
and the subsequent need for IVF. Unexpected age-related infertility
created emotional and financial stressors for participants; ‘As a
woman, your fertility is going to decrease, and you can’t just think
that, “Oh, I’ll just go do IVF”. It’s not foolproof, it’s not easy, and
it’s expensive’. Because of their ages, many of the women attempting
to conceive were urged by their practitioners to ‘go straight to IVF’; a
procedure that participants initially considered to be costly and
extreme. Half of the participants successfully conceived and gave
birth after only one cycle of IVF. Nonetheless, most were presented
with poor statistical prognoses during treatment, which led them to
later acknowledge how close they had been to not being able to
conceive a child. As a result, themes of ‘luck’ and appreciation perme-
ated discussions of having children at a later age via IVF. These experi-
ences led many men and women to express enhanced appreciation
for their children after facing the risk of not having children at all; as
this man recounted: ‘It’s just been a gift. I feel so lucky. I mean, I
just feel so, not religious, but I feel so blessed just to have this experi-
ence. I’m just so grateful’. This woman described how her infertility
influenced her feelings about her child: ‘I think that we just really
appreciate the fact that we were able to have a child at this age, espe-
cially knowing what we know that the statistics aren’t that great and
that there are so many people who go through IVF multiple times
and never conceive . . . Sometimes we look at our son and just think,
“Gosh, how did we get so lucky?”’

Lack of physical energy
Over a third of women and a quarter of men cited the lack of physical
energy they experienced as later-life parents. Noting the substantial
demands of raising children, participants reported feeling depleted
and they imagined having more vigor for parenting if they were

…………………………………………………………………………….

Table III Disadvantages of first-time parenting over
age 40 using IVF.

Women (n 5 65),
(%)

Men (n 5 42),
(%)

Infertility and the need for
IVF

48 17

Less energy 38 26

Less lifetime with children 31 19

Smaller family size 17 2

Stigma of being ‘Older
Parents’

12 19

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younger. A mother mused: ‘I wish I was 10 years younger, then I
wouldn’t be so pooped out by the end of the day. I’d have more
energy to keep up with my daughter, but I’m tired’. Some were con-
cerned about maintaining physical strength as their children age: ‘I
think we’ll still be able to go out and do outdoor activities with him
when he’s a young man or a growing teen. I want to be in somewhat
good shape’. However, in contrast to this desire, many parents noted
that their personal fitness efforts had diminished due to parenting
demands.

Less time with children
Another disadvantage cited by almost a third of women and a fifth of
men was the calculation that participants would have less of their total
lifetime to spend with their children. While feeling positive about their
own projected health and life spans, they simultaneously reflected on
having children later with a sense of loss. As this father said: ‘By the
time they graduate from high school, I’ll be in my seventies…I will
probably be pretty long lived because our family has a good history
of it, but I won’t see a lot of their adult life’. Some expressed concerns
that they would not live long enough to see their grandchildren.

Participants acknowledged that their chances of becoming ill or
dying were higher due to their ages, a risk that came into focus
largely only after their children were born. As one mother said: ‘I
guess that we’ll be really old when the kids are still young, I just
hope that I’ll be healthy long enough for them to really be grown
up and kind of secure as adults before we die’. While concern
about being healthy long enough for children to reach adulthood
was common, many acknowledged the uncertain nature of life at
any age: ‘You realize that they aren’t going to have quite as many
years [with you]. . . . But you know, something could happen to me
tomorrow and that could be the end of it’.

Smaller family size
A related consequence of later-life parenting was that women had
fewer children than they wished for, with two-thirds of participating
families having only one child. Despite preferring the idea of a sibling
for their single children, only one-third of participants made additional
attempts at conception with IVF predominantly because of poor prog-
noses, the substantial demands of parenting at a later age or having
had twins in their first IVF pregnancy. This woman described her
regret: ‘You know, if I had started earlier, I would have loved to
have had another child, to have two, but we didn’t and that’s the
way it is . . . We used up all my eggs’. Another woman situated her
disappointment over not having more children in a larger societal
context: ‘I’m gonna be 43. So there’s a part of me that’s resentful. I
just feel like the way the world is now, by the time, as women, that
we’re really ready . . . in a good marriage or relationship, and financially
we can do it, and all of our ducks are as much in a row as they can be
. . . we’re 42 . . . And so I think it’s not fair’. Some, such as this man,
perceived risks to the mother and/or potential child and did not
want to ‘press their luck’ by having additional children at their age:
‘When we thought about the second child, then the same thing
came up again. . . . We were very lucky to have a very happy,
normal child. Is the second one gonna be like that?’

Others made no additional attempts at children due to self-
perceptions of being too ‘old,’ concerns about the increased physical

and financial demands of having more than one child and the potential
stigma to their children of having older parents. This woman described
their decision-making process: ‘When we are 60 [our son] will
graduate from high school or college. It’s a very different perspective
than when you are a younger parent. So we are conscious. For
[Husband] that was the reason not to get a second child because
then he and I will be even older’. Men generally did not report dissat-
isfaction with family size.

Anticipating age stigma
Almost a fifth of men but fewer women expressed concerns about
future stigma for themselves and their children due to age. Women
in particular remarked that they ‘look young’ and stay active so
people cannot tell their chronological age from their appearance.
Nonetheless, they did anticipate that as their children get older their
age as parents would become more visible and their children would
be stigmatized as a result. This woman imagined: ‘I think now
maybe people don’t think, ‘That’s an older parent.’ The older we
get, and then he will be in high school, it will be more apparent.’ A
theme cited by women and especially men was anticipation of being
over 60 when their children graduated from high school, which for
many was emblematic of the wider generation gap as older parents.
For example, as this man predicted: ‘When my son is graduating
from high school I’m going to be about 60 years old, and that’s prob-
ably a lot older than the other dads . . . I’m going to be getting near a
period of time where I’m wanting to retire and he’s just going to
college. So it just concerns me that I don’t want to be old when
he’s still that young’.

Optimal age for parenting
Overall, our participants concluded that the advantages of later par-
enting clearly outweigh the disadvantages. Nevertheless, approxi-
mately two-thirds of both men and women expressed the opinion
that the optimal age for having children was �5 – 10 years younger
than they had conceived and only 10% concluded that the optimal
age was over 40. The responses to the question addressing the
optimal age to have children are presented in Table IV. Most acknowl-
edged that they could not or would not have made a different child-
bearing decision given their individual and unique life circumstances.
However, in retrospect, many women stated that they would have
wanted to have children earlier if they had met their partner
sooner; as this woman put it: ‘I think if I could have written out the
story of my life, I would have met him younger, and I probably
would have had children maybe at 35 . . . . My life trajectory would

…………………………………………………………………………….

Table IV Perception of optimal age for first-time
parenting by gender.

Women (n 5 64), (%) Men (n 5 36), (%)

20s 11 19

Early 30s 41 31

Mid-30s 17 14

Late-30s 22 25

40s 9 11

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have been totally different. But I think having them in your mid-30s is
probably ideal because there’s a lot less fear about the decline in
fertility’. Some felt that younger parenting is better biologically,
particularly for women, while older parenting is better socially; for
example: ‘Your body’s made to have kids between 14 and 24, but
financially, emotionally, intellectually, I’m way better off now’. Yet
the majority of participants also endorsed the concept that the
timing of childbearing is an individual and contextual undertaking and
that the best time to have children is ‘when you are ready for them’.

Very few men but over a quarter of women reported that they
would have changed their childbearing age because of age-related
infertility. This man noted: ‘I think for a woman maybe mid-30s so
you don’t necessarily have to jump through all the IVF hoops, and I
think for man it could be older’. When discussing the optimal age
for women to have children, both men and women cited the age
range of 30 – 35 as optimal for both biological and social reasons; as
this woman summarized: ‘I think for both men and women . . . . Let
your 20 s be about figuring out who you are and enjoying life and
hopefully figuring out your career a little bit. And then 30 to 33
seems like the right time to really try to have kids’. Another woman
noted: ‘Anything after 35, there starts to be both [fertility] statistics,
and also energy drops. So, yeah, early-mid 30s, it gets really
optimal’. Generally parenting too young or too old was perceived as
undesirable. Younger parents were often characterized as unprepared;
as this woman noted: ‘I think younger parents in their 20 s, they are
stressed out, financially stressed out, work stressed out, time-wise
stressed out.’ Conversely, having children near retirement age was
considered irresponsible, as this man explained: ‘If you’re going to
be dead whenever your kid is out of high school, that’s probably
too late. It’s not a biological thing; I don’t think it’s great for the kid
to have so much of their life without that parent’.

Discussion
Among our cohort of first-time parents after age 40, participants
evoked many of the commonly acknowledged reasons for ‘delayed
childbearing’, i.e. career development, accumulating financial
resources and finding an appropriate partner (Heck et al., 1997; Ham-
marberg and Clarke, 2005; Ryan et al., 2005; Benzies et al., 2006;
Lampic et al., 2006; Tough et al., 2007; Willett et al., 2010). Becoming
established in careers before childbearing enabled participants to accu-
mulate financial resources and workplace flexibility which then pro-
vided more time to focus on their children, which supports findings
in other studies of motherhood and career and finances (Joshi,
2002; Amuedo-Dorantes and Kimmel, 2005; Browning, 2007). The
men in this study who had second families reported higher levels of
engagement and enjoyment of parenting compared with earlier in
their lives when they were more focused on career building.

Our participants cited their relationship with their partner as an
advantage in later parenting, due in part to their having chosen part-
ners who they imagined would be willing to co-parent, reflecting a
gender equity family model (McDonald, 2000; Simpson, 2009).
While this expectation of partner engagement may serve to validate
their partnership trajectories, Bornstein et al.’s (2006) detailed psycho-
logical study of first-time mothers in the USA ranging from age 13 to
42 did find that while older mothers had less familial support for

parenting than younger mothers, they had greater partner/spousal
support.

Both men and women described their accumulation of experience,
self-knowledge and emotional preparedness as girding them against
any possible regret resulting from the change in lifestyle perceived as
accompanying childbearing. This notion that people timed their child-
bearing in order to first achieve a foundation of self-realization and
fulfillment has been explained as reflecting a post-materialist values
framework (Proudfoot et al., 2009; Simpson, 2009). This framework
posits that people organize their lives according to individual ideals
of fulfillment in place of community or religious mores. Our cohort
embraced ideals of self-realization as also providing benefits to their
children. Both men and women contended that their maturity and
life experiences made them better parents than they could have
been earlier in their lives, and contributed to their enjoyment of
most aspects of parenting. In fact, their later disappointment in
having less anticipated lifetime with children may confirm the degree
to which they appreciated their parenting experiences.

By design, participants in our cohort had successfully conceived chil-
dren following infertility, so no couple remained childless. Despite
their success, the major disadvantages of later parenting cited by
women were infertility, the need to utilize IVF and the risk of having
been biologically childless (Browning, 2007). Awareness of age-related
infertility was low despite the advanced education levels among this
group (Friese et al., 2006). A related disadvantage was smaller
family size resulting from age-related infertility or from choosing to
have fewer children due to physical and social effects of aging. In the
USA, most families desire and have two children (Hagewen and
Morgan, 2005), in contrast to our cohort who did not achieve their
desired family size. Such relinquishment of fertility intentions has
been associated with distress (White and McQuillan, 2006).

Other drawbacks to later parenting were less total lifetime available
to be with their children, a perceived lack of energy compared with
their younger selves, and anticipated future stigma from being older
parents to children in high-school. Browning also found concerns
about lack of energy and staying healthy (Browning, 2007). In her quali-
tative study of first-time mothers over age 30, Shelton described nar-
ratives of personal ‘loss’ and ‘isolation’ alongside those about
‘personal growth’ and ‘maturity’(Shelton and Johnson, 2006). In
contrast, themes of loss among our cohort revolved more around lim-
itations on family size and reduced lifetime spent with children than on
personal constraints. The experience of infertility and the 10-year age
difference between cohorts may explain these differing interpretations
of loss and the relative happiness of our older parents with the parent-
ing experience.

The citation of advantages of later-parenting by both men and
women far outweighed the percentage referencing disadvantages.
Yet when asked about the optimal age for parenting, all but 10% of
men and women identified an age 5 – 10 years earlier than they had
conceived. Approximately, three-quarters of men and women ima-
gined that first-time parenting in the 30s offered many of the benefits
of older parents such as career flexibility, experience and financial
security, but would avoid the disadvantages of later conception,
particularly age-related infertility and resulting smaller family sizes.
Many parents made a distinction between a biological age that is
optimal for having children (younger than 30) and a social age that
is optimal for parenting (older than 35). Similarly Dion’s psychological

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study of expectant mothers emphasized a split between ‘physical’ and
‘psychological preparedness’ of younger and older parents (Dion,
1995). Many participants stated that, biologically, men’s optimal age
for parenting could be later than for women (Balasch and Gratacós,
2011), but nonetheless recommended men also begin childbearing
at a younger age due to the physical and energetic demands of
parenting.

Most participants strongly believed that childbearing later in life
made them better parents than they would have been earlier. The
available literature on effects of later-parenting supports our partici-
pants’ belief that waiting until age 30 has psychological or social ben-
efits for parents and their children (Joshi, 2002; Mirowsky and Ross,
2002; Bornstein et al., 2006). However, literature also contrasts our
participants’ expectations that they were even better parents after
age 40, citing either no improved effects beyond age 30 or negative
psychological and health effects (Bewley et al., 2005; Mirowsky,
2005; Balasch and Gratacós, 2011). Infertility and the subsequent
use of IVF to conceive may have had a positive impact on parenting
experiences in our cohort compared with these studies. Feelings of
being ‘lucky’ to conceive at all and their greater ‘appreciation’ for
their children may contribute to their unexpected enjoyment of par-
enting and reported positive family dynamics.

Due to the self-selected cohort and the specific eligibility criteria of
our study, the ability to generalize these findings may be limited. It also
may be possible that couples with a positive experience of late parent-
ing were more likely to be willing to participate. We intentionally
recruited parents who had their first children both at the outer repro-
ductive age limits and after IVF in order to explore the full implications
of ‘delayed parenting’. The resulting cohort consisted of two-parent
households and single mothers with a relatively high socio-economic
status. Their demographic descriptors are consistent with others
who use IVF in the USA (Hammoud et al., 2009). However, their
median income was 3 – 4 times higher than the average US family,
which may bias their largely positive parenting experiences. In addition,
the study was described to participants as a study of ‘later parenting’.
This may have influenced participant responses to the questions; as
adult aging is generally stigmatized in the US (Palmore, 2004) partici-
pants may have framed their responses more positively in an
attempt to deflect any anticipated age-related stigma on the part of
the research team. Finally, the average age of first children was 3
years and the oldest child resulting from IVF was age 10; thus partici-
pants were mostly parents of young children whose experiences may
significantly change as time passes.

Conclusion
While the expected benefits of later parenting such as career flexi-
bility, financial stability, maturity and committed co-parenting, did in
fact materialize for this cohort, there were drawbacks that had been
unanticipated prior to becoming parents. These disadvantages had
enough impact on the conception and parenting experience that the
majority of participants in hindsight identified an optimal age for par-
enting that was 5 – 10 years earlier than they conceived their first
child. Parenting in their 30s was imagined to reflect a compromise
that maximized the financial and emotional advantages of later parent-
ing while minimizing the risks of age-related infertility,
smaller-than-desired family sizes, lack of energy, less lifetime spent

with their children and the potential for age-related stigma. New or
follow-up research with first-time parents over age 40 via IVF who
have teen-age or older children and from a demographic sample
closer to the socio-economic US median would help complete under-
standings of the range of experiences as both the children and parents
age.

Authors’ roles
K.M.D., Y.B. and R.D.N. were integral to the conception and design of
the research, the analysis and interpretation of the data, drafting and
revising the article and had final approval of the published version.
K.M.D. also contributed to acquisition of the data.

Funding
This study was funded by a grant from the National Institute of Child
Health and Human Development entitled Late Parenting & Biotech-
nology: Rethinking Age, Gender, Family, & the Life Course
(1R01HD056202-01A2, 24 August 2009 – 31 July 2011).

Conflict of interest
R.D.N. from the University of California, San Francisco was the prin-
cipal investigator and Y.B. was the co-investigator.

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original article

ANN SAUDI MED 2021 SEPTEMBER-OCTOBER WWW.ANNSAUDIMED.NET274

Correspondence: Dr. Taghreed
Shams · Department of Obstetrics
and Gynecology, King Saud bin
Abdulaziz University for Health
Sciences, Jeddah 22384, Saudi
Arabia · [email protected]
· ORCID: https://orcid.org/0000-
0002-0454-406X

Citation: Shams T, Gazzaz T,
Althobiti K, Alghamdi N, Bamarouf
W, Almarhoumi L, et al. Comparison
of pregnancy outcomes between
women of advanced maternal
age (≥35 years) versus younger
women in a tertiary care center in
Saudi Arabia. Ann Saudi Med 2021;
41(5): 274-279. DOI: 10.5144/0256-
4947.2021.274

Received: June 18, 2021

Accepted: July 2, 2021

Published: October 7, 2021

Copyright: Copyright © 2021,
Annals of Saudi Medicine, Saudi
Arabia. This is an open access
article under the Creative Commons
Attribution-NonCommercial-
NoDerivatives 4.0 International
License (CC BY-NC-ND). The details
of which can be accessed at http://
creativecommons. org/licenses/by-
nc-nd/4.0/

Funding: None.

Comparison of pregnancy outcomes
between women of advanced maternal
age (≥35 years) versus younger women in a
tertiary care center in Saudi Arabia

BACKGROUND: Pregnancy in women aged 35 years or above is gen-
erally considered an advanced maternal age (AMA). AMA is associated
with an increased rate of maternal and neonatal complications.
OBJECTIVES: Assess the effect of AMA on maternal and neonatal out-
comes.
DESIGN: Analytical cross-sectional study of medical records.
SETTINGS: In-patient hospital tertiary care setting in Jeddah.
PATIENTS AND METHODS: All women who attended antenatal care
and delivered at King Abdulaziz Medical City in Jeddah in the first half
of 2018 were included in the study. Outcomes for women 35 years of
age or older were compared with younger women. Significant factors in
a univariate analysis were entered in a multiple logistic regression model
to assess the association between AMA and outcomes.
MAIN OUTCOME MEASURES: Rates of maternal neonatal complica-
tions, analysis of factors associated with advanced maternal, gestational
diabetes mellitus (GDM), cesarean delivery.
SAMPLE SIZE: 1586 women.
RESULTS: Of the 1586 women, 406 were 35 years of age or older
(25.6%), and 1180 were younger than 35 years. The AMA group had a
significantly higher proportion of GDM (32.0% versus 13.2%, P<.001).
The adjusted odds ratio (OR) for GDM was 2.6 (95% CI 2-3.5, P<.001.)
compared with younger women in the multivariate logistic regression
analysis. Older women had a higher rate of cesarean delivery (43.6%
versus 30.8%, P<.001). The adjusted OR for cesarean vs. vaginal delivery
was 1.5 (CI 1.2-1.9, P=.002).
CONCLUSION: Pregnancy in women 35 years or older was associated
with an increased risk of GDM and cesarean delivery.
LIMITATIONS: Cross-sectional design, small sample size, single hospital.
CONFLICT OF INTEREST: None.

Taghreed Shams,a Tala Gazzaz,b Khalda Althobiti,c Nouf Alghamdi,d Waleed Bamarouf,b Lujain
Almarhoumi,a Hashem Alhashemie

From the aDepartment of Obstetrics and Gynecology, King Saud bin Abdulaziz University for Health Sciences, Jeddah, Saudi Arabia;
bCollege of Medicine, King Abdulaziz University Hospital, Jeddah, Saudi Arabia; cCollege of Medicine, Taif University, Taif, Saudi Arabia;
dDepartment of Laboratory Medicine, Al Baha University, Al Baha, Saudi Arabia; eDepartment of Internal Medicine, King Abdulaziz Medical
City, Jeddah, Saudi Arabia

original articlePREGNANCY OUTCOME IN AMA

ANN SAUDI MED 2021 SEPTEMBER-OCTOBER WWW.ANNSAUDIMED.NET 275

T
he term advanced maternal age (AMA) applies to
childbearing women aged 35 years and older.1 In
recent decades, having children at an older age

has been an increasing trend within developed coun-
tries.2,3 Many factors, such as the presence of safe and
effective contraception, higher education and demand-
ing career opportunities, advances in assisted repro-
ductive techniques, financial insecurity, and unstable
relationships have contributed to the trend of delaying
pregnancy.3,4

In the year 2013 in the United Kingdom, 20% of
deliveries were among women aged 35 and older, and
4% were among women aged 40 years old and older
compared with 6% and 1%, were respectively, in 1980.2
This increase in AMA has also been observed in many
parts of Asia and in Portugal.5 In Saudi Arabia, the rate
of AMA was 17% in 2017.6 Pregnancy in women at an
AMA is associated with an increased risk of miscarriage,
preeclampsia, gestational diabetes (GDM), small for
gestational age (SGA) neonates, placenta previa,7 ce-
sarean delivery8 and severe maternal morbidity such as
amniotic fluid embolism, obstetric shock, renal failure,
complications of obstetric interventions, and intensive
care unit admission. Similar associations were observed
for fetal and infant outcomes.9

A study from the eastern province of Saudi Arabia
that included 2517 primigravidas reported that only 8%
of women were older than the age of 35 years. Women
at an AMA had more diabetes mellitus, preterm labor,
and cesarean deliveries. In addition, babies of older
mothers had lower birthweights.10 Our study aimed to
determine the rate of AMA and the maternal and neo-
natal outcomes associated with AMA at King Abdulaziz
medical city in Jeddah (KAMC-J), Saudi Arabia.

PATIENTS AND METHODS
This cross-sectional study included all pregnant women
who attended antenatal care and delivered in KAMC-J,
Saudi Arabia, in the 6-month period between January
and June 2018. The study compared pregnant women
who were aged 35 years or older at the time of de-
livery (AMA group) and the control group included
pregnant women who were younger than 35 years
(non-AMA group). After ethical approval was acquired
from the Institutional Review Board of King Abdullah
International Medical Research Center, data were col-
lected from electronic medical records. The two groups
were compared regarding their demographic data,
medical history, and different maternal and neonatal
outcomes. Demographic data included maternal age
at delivery, body mass index (BMI), gravidity, and par-
ity, pre-pregnancy maternal medical conditions (dia-

betes, hypertension, and hypothyroidism). Pregnancy
outcomes included GDM, diagnosed according to
the American Diabetes Association.11 Hypertensive
disorders in pregnancy were defined according to the
American College of Obstetricians and Gynecologists12
as placenta previa, induction of labor using prostaglan-
din or oxytocin, placental abruption, preterm labor, ce-
sarean delivery, and postpartum hemorrhage.

Neonatal outcomes included SGA, defined as birth
weight less than 2.5 kg, neonatal mortality, 1- and
5-minute Apgar scores, admission to intensive care
unit, intrauterine fetal death (IUFD), and congenital
anomalies. Patients who did not have antenatal care in
KAMC-J or were not screened for GDM were excluded
from the study.

Statistical analysis was performed using IBM SPSS
software (version 24, IBM, Armonk, NY: IBM Corp).
The chi-square test was used to assess the association
between different pregnancy outcomes and AMA as
a categorical variable. Pregnancy outcomes that were
significantly associated with AMA were tested using
multiple logistic regression.

RESULTS
Of 1677 women who had antenatal care and gave
birth at KAMC-J, Saudi Arabia, 1586 women met the
inclusion criteria. Ninety-one women were excluded
because they did not have antenatal care at KAMC-J.
Twenty-five percent (25.6%) of the study population
was 35 years of age or older. The median ages were
37.5 years (range, 35-48) for the older women and 27
years (range, 17-34) for the younger women (P<.001).
BMI was 31 kg/m2 (range, 14-62) for the older women
and 28 kg/m2 (range, 15-65) for the younger women
(P<.001). According to BMI at the time of delivery, most
women were overweight or obese: 83% and 70% in the
study group and control group, respectively (Table 1).
Only 6% of the women in the AMA group were preg-
nant for the first time while 38% of the younger group
was pregnant for the first time. Type II diabetes, chronic
hypertension, and hypothyroidism were more prevalent
in the study group (Table 2).

Pregnancy in women of AMA was more likely to be
complicated by GDM. Older women were more likely to
have a cesarean delivery than younger women. Other
maternal outcomes such as hypertensive disease of
pregnancy, placental abruption, placenta previa, oligo-
hydramnios, and polyhydramnios were not statistically
significant between the two groups. Neonatal complica-
tions such as low 1- and 5-minute Apgar scores, SGA,
IUFD, neonatal disease, malformation, and admission to
NICU were similar in the two groups (Table 3).

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Table 1. Maternal characteristics of 1586 women in the study.

Characteristics AMA (n=406)
Non-AMA
(n=1180) P value

Median age (range) 37 (35-48) 27 (17-34) .001a

Body mass index (kg/m2)

Underweight (<18.5) 3 (1.0) 30 (2.5)

.001a
Normal (18.5-24.9) 59 (14.5) 335 (28.4)

Overweight (25-29.9) 113 (27.8) 413 (35.0)

Obese (≥30) 225 (55.4) 397 (33.6)

Parity

Median 4 1

Nulli 25 (6.2) 448 (38.0)
<.001

Multi 381 (93.8) 732 (62.0)

Thyroid function

Normal 360 (88.7) 1111 (94.1)
<.001

Low 46 (11.3) 69 (5.8)

Diabetes

Non-diabetic 383 (94.3) 1173 (99.4)

<.001a DM II 19 (4.7) 3 (0.3)

DM I 4 (1.0) 4 (0.3)

Chronic hypertension 11 (2.7) 7 (0.6) <.001

Data are number (%) unless otherwise noted. aFisher Exact test.

Using multiple logistic regression to adjust for con-
founder that may affect the rate of GDM and cesarean
delivery such as BMI, multiparity, hypothyroidism, SGA,
preterm labor, hypertensive diseases of pregnancy and
labor induction, GDM and cesarean delivery were signif-
icantly associated with AMA (Table 4). The factors asso-
ciated with GDM were BMI more than 25 kg/m2. In other
words, women aged 35 years or older with BMI ≥25 kg/
m2 were 70% more likely to have GDM, and multiparous
women of AMA during pregnancy were 80% more likely
to have GDM (Table 5). Factors associated with cesar-
ean delivery were BMI more than 25 kg/m2, GDM, and
SGA. Induction of labor decreased the risk of cesarean
delivery (Table 6).

DISCUSSION
The rate of AMA in this study (25.6%) was higher than
the 17% rate reported in the northern region of Saudi
Arabia13 but consistent with 23% found by a large de-
mographic study done in Riyadh,14 and another study
in the USA.15 Although there is a rising trend to delay
childbearing secondary to improving access to educa-
tion, career opportunities, contraception and assisted
reproductive techniques,8 only 6.2% of women of AMA
in this study were pregnant the first time. This finding
is in agreement with the finding of Fayed et al.14 They
found 3.4% of their AMA population were primigravi-
da and 70% were para five or more. This means Saudi
women choose to have children after the age of 35
years to complete their family rather than delaying the
onset of motherhood.

The rate of obesity was high in the whole cohort (56%
in the AMA group and 33% in the younger group). In a
population-based study including 10 735 Saudi partici-
pants aged 15 years or older,16 there were high rates of
obesity across all segments of the population, reaching
33.5% of women and 24.1% of men. Among women,
the risk of obesity increased with age, being married,
having been diagnosed with a chronic condition, being
hypertensive, and having less education.

The rate of GDM in the AMA group was high, reach-
ing 32% in comparison to the rate of 22% in Korea and
14% in the US.17,18 This high rate is most likely related
to the high rate of obesity and ethnic background.19

The estimated risk of GDM was 2.6 times higher than
younger women in our study, which is higher than risk
estimated by a large retrospective study in the UK by
Khalil et al8 (OR 1.88, 95% CI: 1.55-2.29; P<.001), but
similar to the OR of 2.85 estimated by a meta-analysis
of 28 studies looking at cesarean delivery as a secondary
outcome in AMA.2

Table 2. Maternal pregnancy outcomes.

Outcome AMA (n=406)
Non-AMA
(n=1180) P value

Gestational diabetes 130 (32) 156 (13.2) <.001

Hypertensive disease
of pregnancy

Gestational 4 (1.0) 15 (1.0) .99a

Preeclampsia 9 (2.2) 38 (3.0)

Antenatal
complications

Abruption 1 (0.2) 7 (0.6) .8a

Placenta previa 5 (1.2) 11 (0.9)

Oligohydramnios 1 (0.2) 4 (0.3)

Polyhydramnios 3 (0.7) 9 (0.8)

Induced labor 57 (14.0) 225 (19.1) .02

Cesarean delivery 177 (43.6) 363 (30.8) <.001

Postpartum
hemorrhage

43 (10.6) 103 (8.7) .3

Data are number (%). aFisher exact test.

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Table 3. Fetal outcomes.

Outcome AMA (n=406) Non-AMA(n=1180) P value

Preterm labor 37 (9.0) 112 (9.5) .8

Small for gestational
age

47 (12.0) 159 (14.0) .3

Intrauterine fetal
death

2 (0.5) 14 (1.2) .3a

1 minute Apgar
score less than 7

23 (6.0) 65 (6.0) .9

5 minute Apgar
score less than 7

8 (2.0) 22 (2.0) .9

Admission to NICU 29 (7.0) 70 (6.0) .4

Neonatal diseaseb 110 (27.0) 333 (29.0) .6

Syndromes

Down 3 (0.7) 2 (0.2)

Sanjad Sakati 0 1 (0.1)

Noonan 0 1 (0.1)

Malformations

Musculoskeletal 30 (7.4) 74 (6.3)

Cardiac 6 (1.5) 20 (1.7)

Central nervous
system

1 (0.3) 4 (0.4)

Genital 9 (2.2) 25 (2.1)

Renal 1 (0.3) 5 (0.4)

Gastrointestinal 2 (0.5) 5 (0.4)

Multiple 3 (0.7) 8 (0.7)

Total 52 (13.0) 141 (12.0)

Syndrome and
malformations

55 (14.0) 145 (12.0) .6

Data are number (%). aFisher’s Exact test. bRespiratory distress syndrome, transient tachypnea of
newborn, neonatal jaundice and polycythemia

As expected, the incidence of cesarean delivery was
higher in the AMA group (44% versus 31% in the Non-
AMA group). This rate is similar to the rate of 40% found
in central Saudi Arabia by a recent cross-sectional study
published by Alshehri et al.20 After adjusting for con-
founders such as parity, obesity, gestational age at the
time of delivery, induction of labor, and GDM, women of
AMA are 50% more likely to have cesarean delivery than
younger women (OR 1.5, P<.003, CI 1.1-1.9). This risk
is similar to the estimated risk by Japanese population-
based study published by Ogawa et al7 reported a rela-
tive risk of 1.18, 1.4 and 1.53 for women 35-39, 40-44,
and 45-49 years of age, respectively.

In women of AMA, induction of labor decreased the
risk of cesarean delivery by 30% in our study (OR 0.7,
CI 0.5-0.9, P<.03). However, a recent meta-analysis of
of six randomized clinical trials including 958 patients
with low heterogeneity, comparing induction of labor
with expectant management in singleton pregnancies
at term in women of AMA, showed no significant differ-
ence;21 The pooled odds ratio was 0.97 (95 % CI=0.86-
1.1). Most likely the estimate from the meta-analysis is
more accurate.20 The finding of our study that induction
of labor decreases the risk of cesarean delivery may well
be due to type I error (i.e, the statistically significant dif-
ference is due to chance and not due to real difference).

A recent cross-sectional study22 including 3942 wom-
en found a higher rate of preeclampsia in AMA (5.1%
in comparison to younger women 3.7% OR 1.4 (95%
CI 1.1-1.9, P=.03). Our data did not find a difference
between the two groups. The rate of preeclampsia in
our population was low (3%) which is in agreement with
Subki et al23 study done in the same region. They looked
into the rate of preeclampsia among 9493 deliveries
and reported a rate of 2.4%.

Our study did not find a difference in the selected
neonatal outcome, most likely due to the small sample
size. The incidence of fetal anomalies was high in both
groups: 13% in the AMA group and 12% in the non-
AMA group. This rate is higher than the reported inci-
dence of 4.5% in Riyadh.24 We expect the reason for this
high incidence is the fact KAMC-J is the largest referral
center for fetal anomalies in the Western province of
Saudi Arabia.

The strength of this study includes the use of elec-
tronic hospital medical records, accurate assessment
of gestational age, the examination of a wide range of
adverse pregnancy outcomes, and the use of multivari-
able logistic regression analysis to control for risk factors
associated with each adverse outcome. The limitation of
our study is the small sample size from a single hospital.

In conclusion, the rate of AMA was 25.6% in women

who gave birth at our center. Pregnancy in women 35
years or older was associated with an increased risk of
GDM and cesarean delivery. Future population-based
studies powered to assess risk related to the induction
of labor and neonatal outcome are recommended.

Acknowledgments
The authors wish to sincerely thank Abdulrahman
Alsamadani, Haitham Alasmari, Raneem Albalawi, Amal

Aljawi, Bsaim Altirkistani, and Abeer Siddiqi for assist-
ing in the data collection.

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Table 4. Multivariate logistic regression with advanced maternal age as the dependent variable (n=1545).

Variables
Unadjusted Adjusted

Odds ratio P value 95% C.I. Odds ratio P value 95% C.I.

Body mass index (≥25
kg/m2)

2.5 .001 1.8-3.3 1.7 .001 1.3-2.4

Multiparity 9.3 .001 6.1-14 7.8 .001 5-12

Hypothyroidism 2.1 .001 1.4-3.0 2.0 .001 1.3- 3.2

Labor induction 0.7 .02 .5-.9 .9 .6 .6-1.3

Cesarean delivery 1.7 .001 1.4-2.2 1.5 .002 1.2-1.9

Gestational diabetes 3.4 .001 2.6-4.4 2.6 .001 2-3.5

Model summary: -2 log likelihood:1521.81, Cox and Snell R square: .152, Nagelkerke R square: .225

Table 5. Multivariate logistic regression with gestational diabetes as the dependent variable (n=1545).

Unadjusted Adjusted

Predictors Odds ratio P value 95% C.I. Odds ratio P value 95% C.I.

Body mass index (≥25
kg/m2)

2.1 .001 1.5-2.9 1.7 .003 1.2-2.4

Multiparity 2.6 .001 1.9-3.7 1.8 .002 1.2-2.5

Advanced maternal age 3.4 .001 2.6-4.4 2.7 .001 2 -3.6

Model summary: -2 log likelihood: 1408.84, Cox and Snell R square: .057, Nagelkerke R square: .093

Table 6. Multivariate logistic regression with cesarean delivery as the dependent variable (n=1522).

Predictors
Unadjusted Adjusted

Odds ratio P value 95% C.I. Odds ratio P value 95% C.I.

Body mass index (≥25
kg/m2)

1.5 .002 1.1-1.9 1.4 .01 1.1-1.8

Advanced maternal age 1.7 .001 1.4-2.2 1.5 .002 1.1-1.9

Gestational diabetes 1.7 .001 1.4-2.3 1.5 .003 1.1-2

Small for gestational
age

2.6 .001 2.0-3.5 2.3 .001 1.6-3.3

Preterm labor 2.2 .001 1.6-3.1 1.3 .2 0.8-2

Labor induction .7 .01 .5-.9 0.7 .02 .5-.9

Hypertensive disorders
of pregnancy

1.9 .01 1.2-3.1 1.6 .1 .9-2.7

Model summary: -2 log likelihood:1925.380, Cox and Snell R square: .055, Nagelkerke R square: .076

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REFERENCES

Acta Obstet Gynecol Scand. 2020;99:459–468. wileyonlinelibrary.com/journal/aogs  |  459© 2019 Nordic Federation of Societies
of Obstetrics and Gynecology

Received: 19 May 2019  |  Revised: 4 November 2019  |  Accepted: 6 November 2019
DOI: 10.1111/aogs.13769

O R I G I N A L R E S E A R C H A R T I C L E

Pregnancy complications and risk of preterm birth according
to maternal age: A population-based study of delivery
hospitalizations in Alberta

Natalie V. Scime1  | Katie H. Chaput1,2,3 | Peter D. Faris1 | Hude Quan1 |
Suzanne C. Tough1,3 | Amy Metcalfe1,2,4

Abbreviations: aRD, adjusted risk difference; aRR, adjusted risk ratio; DAD, discharge abstract database; iPTB, iatrogenic preterm birth; PAF, population-attributable fraction; PTB,
preterm birth; RD, risk difference; RERI, relative excess risk due to interaction; RR, risk ratio; sPTB, spontaneous preterm birth.

1Department of Community Health
Sciences, Cumming School of Medicine,
University of Calgary, Calgary, AB, Canada
2Department of Obstetrics & Gynecology,
Cumming School of Medicine, University of
Calgary, Calgary, AB, Canada
3Department of Pediatrics, Cumming School
of Medicine, University of Calgary, Calgary,
AB, Canada
4Department of Medicine, Cumming School
of Medicine, University of Calgary, Calgary,
AB, Canada

Correspondence
Natalie V. Scime, University of Calgary,
Owerko Center in the Child Development
Center, 2500 University Drive NW, Calgary,
T2N 1N4 Alberta, Canada.
Email: [email protected]

Funding information
No external funding was sought for this
research. NVS is supported by a Canadian
Institutes of Health Research Canada
Graduate Scholarship Doctoral Award. AM is
supported by a Canadian Institutes of Health
Research New Investigator Award.

Abstract
Introduction: Pregnancy-related medical complications are associated with a 2- to
5-fold increased risk of preterm birth (PTB), but the nature of this etiologic relation in
context with maternal factors remains poorly understood. Previous studies have gen-
erally treated maternal age as a confounder but overlooked its potential as an effect
modifier, whereby the magnitude of the effect of complications on PTB could dif-
fer significantly across age groups. We investigated whether advanced maternal age
(≥35 years) modified the association between pregnancy complications and PTB, and
compared population-attributable fractions of PTB from complications in women
older vs younger than 35 years.
Material and methods: We analyzed population-based, cross-sectional data from the
Alberta Discharge Abstract Database for women aged 18-50 years with singleton live
births in hospital between 2014 and 2017 (n = 152 246). Complications were preec-
lampsia, gestational diabetes, and placental disorders identified using diagnostic
codes. Outcomes were spontaneous (sPTB) or iatrogenic (iPTB) PTB before 37 weeks
of gestation. We estimated risk ratios and risk differences using modified Poisson and
log binomial regression, respectively, adjusting for confounders (pregnancy history,
comorbidities). Population-attributable fractions estimates were calculated from risk
ratios. Age modification was tested using interaction terms and Z-tests.
Results: Prevalence of advanced maternal age was 19.2%. Pregnancy complications
and s/iPTB were more common among women aged ≥35 years. Age modified the risk
of PTB from preeclampsia only, with risk differences of 9.9% (95% CI 7.2%-12.6%) in
older women vs 6.1% (95% CI 4.8%-7.4%) in younger women (P-interaction = 0.012) for
sPTB, and 29.5% (95% CI 26.0%-33.1%) vs 20.8% (95% CI 18.9%-22.6%, P-interaction
<0.001) for iPTB. Population-attributable fractions of s/iPTB types for all complica-
tions were consistently 2%-5% larger in women aged ≥35 years, and significantly larger
for preeclampsia (sPTB: 5.1% vs 2.7%, P = 0.002; iPTB: 18.8% vs 14.0%, P < 0.001) and
placental disorders (sPTB: 12.5% vs 8.7%, P < 0.001; iPTB: 13.2% vs 8.9%, P < 0.001).

460  |     SCIME Et al.

1   |   I N T R O D U C T I O N

In the context of childbearing, advanced maternal age is typically
defined as 35 years or older.1 The number of women becoming
pregnant after 35 years for personal (eg, relationship stability),
educational, or financial reasons continues to rise in high-income
countries.1 However, delaying childbearing is not without impor-
tant health considerations. Older women are at greater risk of
obstetric interventions and adverse pregnancy outcomes.2 High-
quality observational studies indicate that advanced maternal
age is an independent risk factor for preterm birth (PTB),2-4 after
controlling for confounders like parity, previous PTB, and socio-
economic status. When born preterm, infants often have substan-
tially higher odds of neonatal morbidity and mortality, suboptimal
development and health problems into childhood, and behaviural
and school difficulties into adolescence.5 On a societal level, the
economic burden of PTB in Canada from birth to 10 years of age
is Can$587.1 million.6

Pregnancy-related complications also occur more frequently
among women aged ≥35 years. Preeclampsia occurs in roughly 3%
of older women and 2% of younger women, representing a 1.5-fold
relative increase in this condition with advanced age.7 Gestational
diabetes is over twice as prevalent in women aged ≥35 years com-
pared with women aged <35 years, with reports of 11% and 5%, re-
spectively.8 Despite differences in presentation, placental disorders
like placenta previa, placenta accreta, and placental abruption occur
more often among older women with adjusted odds ratios ranging
from 2.7 to 3.4 and a baseline risk in younger women of between 2-7
cases per 1000 births.9-11 Importantly, preeclampsia,12 gestational
diabetes,13 and placental disorders11 increase a woman’s risk of PTB,
regardless of her age.

The separate effects of maternal age and pregnancy complica-
tions on PTB have been extensively studied. However, effect modi-
fication from maternal age in the association between complications
and PTB has been poorly described, as age is often treated as a con-
founder and controlled for during analysis. Furthermore, it is unclear
whether the proportion of PTBs attributable to complications dif-
fers in older vs younger women. Thorough knowledge on the impact
of advanced maternal age may enhance the precision of PTB risk

management at the individual (clinical) and population (policy/public
health) levels.

This study aimed to assess whether advanced maternal age mod-
ifies the association between pregnancy complications and PTB,
and compare population-attributable fractions (PAFs) of PTB from
complications in women younger and older than 35 years. We hy-
pothesized that advanced maternal age potentiates the risk of PTB
associated with pregnancy complications, and that PAFs of PTBs
from complications may be higher among older women.

2   |   M AT E R I A L A N D M E T H O D S

We performed a cross-sectional analysis of in-hospital deliver-
ies in Alberta from April 1, 2014 to March 31, 2017, and followed
the RECORD reporting guidelines.14 Data were obtained from ma-
ternal delivery hospitalization records in the provincial Discharge
Abstract Database (DAD). Data in the DAD is abstracted from
medical charts by trained personnel using standardized protocols,
and includes patient demographics, up to 25 diagnostic codes from
the International Classification of Diseases 10th Revision (ICD-10),
and up to 20 procedure codes from the Canadian Classification for
Health Interventions. The DAD has excellent coverage of all provin-
cial births except for home births (<1% of births in Alberta).

We included women aged 18-50 years with singleton live births
(Z37.0, Z38) with >22 weeks completed gestation who delivered in

Conclusions: Of the pregnancy complications studied, advanced maternal age only
modified the association between PTB and preeclampsia, such that older women with
preeclampsia have a higher risk for s/iPTB than younger counterparts. Pregnancy
complications contribute to a sizable proportion of PTBs in Alberta, especially among
women aged ≥35 years. Findings may inform clinical risk assessment and population-
level policy targeting PTB.

K E Y W O R D S

Alberta, discharge abstract database, effect modification, maternal age, pregnancy
complications, premature birth

Key Message

Advanced maternal age (≥35 years) modifies the risk of
spontaneous and iatrogenic preterm birth associated with
preeclampsia, but not gestational diabetes or placental
disorders. The population fractions of preterm birth at-
tributable to these pregnancy complications are consist-
ently higher among older women compared with younger
women.

     |  461SCIME Et al.

an Albertan hospital. Data on stillbirths were not available. Multiple
births were excluded given that they are strongly associated with PTB
and assisted reproductive technology,15 the latter of which is poorly
captured in the DAD. Pregnancy complications included preeclamp-
sia, gestational diabetes, and placental disorders, and were measured
by the presence of corresponding ICD-10 codes in any diagnosis
field. Cases of preeclampsia, including super-imposed preeclampsia,
eclampsia, and HELLP (hemolysis, elevated liver enzymes, low plate-
lets) syndrome, were identified using an algorithm (O11, O14-15) pre-
viously published for describing international trends in hypertensive
disorders of pregnancy.16 Gestational diabetes is diagnosed between
24 and 28 weeks of gestation with universal screening in Alberta, and
cases were identified using an algorithm (O24.4, O24.8) validated in
the Alberta DAD with a sensitivity of 86% and specificity of 99%.17
Placental disorders were operationalized as the presence of placenta
previa (O44), placenta accreta (O43.2), or placental abruption (O45).

Gestational age at birth is recorded in the DAD as weeks of com-
pleted gestation, which was dichotomized at <37 weeks to identify
cases of PTB. We distinguished the type of PTB by using diagnostic
codes to determine labor onset and procedure codes to ascertain
induction use or cesarean delivery;18,19 women who were induced
before delivery or had a scheduled cesarean delivery (without ex-
periencing labor) at <37 weeks were classified as iatrogenic (iPTB),
and the remaining women who delivered at <37 weeks were coded
as spontaneous (sPTB).

Maternal age at delivery was categorized into younger age
(<35 years) and advanced age (≥35 years) according to the clinical
definition.1 To minimize misclassification, concordance for each
woman’s age group was assessed from admission to discharge.
Forty-one women turned 35 during the delivery hospitalization,
as evidenced by classification of younger age upon admission
and older age upon discharge; given that we did not have wom-
en’s dates of birth to discern age at delivery, these records were
excluded.

All analyses were adjusted for parity and past PTBs (primipa-
rous, multiparous without past PTB, multiparous with past PTB),
and maternal comorbidity. Comorbidities were measured using
a modified version of the Obstetric Comorbidity Index, which is
a weighted algorithm for 20 conditions such as physical illness,
pregnancy complications, and substance abuse. This index was
developed in 2013 using US Medicaid data, and subsequently val-
idated in 2015 using the Alberta DAD for ability to predict mater-
nal end-organ damage, prolonged length of stay, and death.20,21 To
eliminate overlap with our study variables, we adapted the index
to exclude preeclampsia, placenta previa, and advanced maternal
age as outlined in the Supplementary material (Table S1). Multiple
gestation was also excluded given our focus on singletons only.
Summary index scores were calculated by summing the weights
(corresponding to risk estimates) for each present condition,20
then categorizing scores into 0 or ≥1. We used this composite co-
morbidity variable instead of individual comorbidity variables to
avoid data sparsity given the highly imbalanced prevalence for
many of these conditions.

2.1 | Statistical analyses

Records with extreme (ie, ≤22 or ≥43 weeks) or missing gestational
age values were excluded. All analyses were stratified by maternal
age group. Obstetric characteristics for the study population were
summarized using descriptive statistics and compared using chi-
squared tests or t tests. First, Poisson regression with robust error
variance was used to estimate risk ratios (RR), and log binomial re-
gression was used to estimate risk differences (RD) for pregnancy
complications and PTB; crude and multivariable adjusted estimates
are reported. We ran three models for each complication-PTB type
association separately on the multiplicative and additive scales: 2
age-stratified models, and one model with the full sample includ-
ing a maternal age interaction term (to assess effect modification).
Next, PAFs were estimated using adjusted RRs from each model
with the PUNAF command, and were compared using z-tests (see
Supplementary material, Table S2 for details and formulae). All
estimates were calculated with 95% CI and statistical significance
was set to P < 0.05. Data cleaning and analyses were performed in
Stata version 15 (Stata Corp., College Station, TX, USA).

We repeated the analyses using maternal age categories of <40
and ≥40 years to determine whether our results were sensitive to
the maternal age cut-point selected. To explore effect modifica-
tion using an alternative approach to interaction terms, we then
deconstructed our full sample models (that included a complica-
tion*age term) for both age cut-points into joint and main effects
on the multiplicative scale and calculated the relative excess risk
due to interaction (RERI). The RERI is a measure of modification
on the additive scale, whereby a value of 0 indicates no modifi-
cation and a value of >1 indicates positive effect modification.22
We also conducted a sensitivity analysis to examine the potential
role of unmeasured confounding (eg, smoking, body mass index,
socio-economic status) by calculating e-values for the associations
studied. An e-value is the minimum strength of association, on the
RR scale, that an unmeasured confounder would need to have with
both the pregnancy complication and PTB, conditional on the mea-
sured covariates, to fully explain away the observed association.23

2.2 | Ethical approval

This study was approved by the Conjoint Health Research Ethics
Board at the University of Calgary (REB13-0760) on 18 November
2018.

3   |   R E S U LT S

Overall, 153 580 singleton live births occurred in an Alberta hospital
between 1 April 2014 and 31 March 2017. After excluding records of
women aged <18 years, with indiscernible age at delivery, or records
containing implausible or missing values, 152 246 women were in-
cluded in this analysis (see Figure 1). With respect to maternal age,

462  |     SCIME Et al.

123 062 women (80.8%) were <35 years and 29 184 women (19.2%)
were ≥35 years. Obstetric characteristics for the study population
are displayed in Table 1. Individual pregnancy complications were
significantly more prevalent among women aged ≥35 years. Older
women were substantially more likely to have at least 1 pregnancy
complication compared with younger women (18.1% vs 9.2%, re-
spectively) and to have sPTB (4.6% vs 3.8%) or iPTB (3.6% vs 2.5%).
Women aged ≥35 years were significantly more likely to be mul-
tiparous, have past PTB, experience an obstetric comorbidity, and
deliver via cesarean section. The most common individual obstetric
comorbidities (and only comorbidities with a prevalence exceeding
1%) were previous cesarean delivery and gestational hypertension
(see Supplementary material, Table S1). Age-related differences in
prolonged maternal length of stay were observed for cesarean birth
(>4 days), but not vaginal birth (>2 days).

Table 2 displays the prevalence of PTB among exposure and ma-
ternal age groups, and Table 3 displays the measures of association
for pregnancy complications and PTB across maternal age groups.
Adjustment for confounders generally attenuated the RRs and RDs
for both types of PTB from pregnancy complications. Significant inter-
action terms on the additive scale indicated age modification for risk of
both sPTB and iPTB from preeclampsia, and for risk of iPTB from pla-
cental disorders. The adjusted RDs (aRD) were higher with advanced
maternal age for preeclampsia (sPTB: 9.9% for women ≥35 years vs
6.1% for women <35 years, P = 0.012; iPTB: 29.5% vs 20.8%, P < 0.001)
and placental disorders (iPTB: 14.1% vs 11.0%; P = 0.021). Maternal
age did not modify the association between gestational diabetes and
sPTB or iPTB. Overall, placental disorders conferred the highest risk
of sPTB (adjusted RR [aRR] 5.1, 95% CI 4.8-5.5) whereas preeclampsia
conferred the highest risk of iPTB (aRR 8.9, 95% CI 8.3-9.6).

Table 4 displays the population fractions of PTB attributable
to pregnancy complications across maternal age groups. The pro-
portions of sPTB and iPTB exposed to each complication (which
was used in estimating PAFs) were consistently higher among
women aged ≥35 years. Pregnancy complications invariably
contributed to larger PAFs of sPTB and iPTB in older women.
For sPTB, age-related differences in PAFs were significant for
preeclampsia (<35 PAF 2.7% vs ≥35 PAF 5.1%, P = 0.002) and
placental disorders (<35 PAF 8.7% vs ≥35 PAF 12.5%, P < 0.001),
but not gestational diabetes (<35 PAF 1.4% vs ≥35 PAF 3.8%,
P = 0.057). Trends were similar for iPTB, whereby age-related
differences in PAFs were significant for preeclampsia (<35 PAF
14.0% vs ≥35 PAF 18.8%, P < 0.001) and placental disorders
(<35 PAF 8.9% vs ≥35 PAF 13.2%, P < 0.001), but not gestational
diabetes (<35 PAF 4.3% vs ≥35 PAF 6.6%, P = 0.121). Overall,
placental disorders were attributable to the largest proportion
of sPTB (PAF 9.6%, 95% CI 8.8%-10.3%) and preeclampsia was
attributable to the largest proportion of iPTB (PAF 15.2%, 95%
CI 14.2%-16.2%).

Sensitivity analyses using a maternal age cut-point of 40 years
are included in the Supplementary material (Table S3). Findings
were similar with the exception of the direction of age modifica-
tion in placental disorders; the aRR for iPTB was lower with ad-
vanced maternal age of 40 years or older (3.4 for women ≥40 vs
5.6 for women <40; P = 0.004). Alternative effect modification
analyses using joint and main effects and RERI are presented in
the Supplementary material (Table S4). The main effects for all 3
pregnancy complications were consistently higher than that of ad-
vanced maternal age, and the joint effects of both exposures were
often larger than either main effect. RERIs for both sPTB and iPTB

F I G U R E 1   Flow diagram of study
population. aWomen were initially
classified as younger age (<35 y) at
admission and re-classified as advanced
age (≥35 y) upon discharge. Given that we
did not have access to women’s dates of
birth, these observations were excluded
to minimize misclassification of maternal
age

Total delivery hospitalization records
for singleton live births in an Alberta

hospital between 1 April 2014 to 31 March
2017

n = 153 580

Total delivery hospitalization records
analyzed

n = 152 246

Maternal age
n = 41 excluded due to inability to

discern age at deliverya
n = 1131 excluded <18 years

Extreme or missing values
n = 162 excluded

     |  463SCIME Et al.

were small to moderate in size (range −0.6 to 2.2) and generally
indicated positive effect modification, but were non-significant at
both age cut-points with the exception of preeclampsia, maternal
age ≥35 years, and iPTB (RERI 1.8, 95% CI 0.3-3.2). Sensitivity anal-
yses examining the role of unmeasured confounding using e-values
are included in the Supplementary material (Table S5). The find-
ings were consistent across maternal age groups: very strong con-
founding (as indicated by large e-values) would be required to fully
explain the associations with PTB types for preeclampsia and pla-
cental disorders, whereas weak confounding (as indicated by small
e-values) could explain away the associations between PTB types
and gestational diabetes.

4   |   D I S C U S S I O N

Using 3 years of population-based data from Alberta, we investi-
gated whether advanced maternal age modified the association
between pregnancy complications and PTB, and compared PAFs of
PTB from complications in women younger or older than 35 years.
As expected, pregnancy complications were more prevalent among
women aged ≥35 years. There was no evidence of age modifica-
tion for risk of sPTB or iPTB from gestational diabetes, but some
evidence of age modification for risk of sPTB and iPTB from preec-
lampsia, with larger aRDs among older women. Advanced maternal
age also modified the risk of iPTB from placental disorders; however,

T A B L E 1   Obstetric characteristics for women aged 18-50 years with singleton live births in an Alberta hospital between April 2014 and
March 2017

Characteristic

Maternal age

P-value

Overall
n = 152 246
% (95% CI)

<35 years
n = 123 062
% (95% CI)

≥35 years
n = 29 184
% (95% CI)

Pregnancy complications

Preeclampsia 1.8 (1.8-1.9) 1.7 (1.6-1.8) 2.3 (2.2-2.5) <0.001

Gestational diabetes 7.3 (7.2-7.5) 5.8 (5.7-6.0) 13.5 (13.2-13.9) <0.001

Placental disorders 2.3 (2.2-2.4) 2.0 (2.0-2.1) 3.4 (3.2-3.6) <0.001

Placenta previa 0.7 (0.7-0.7) 0.6 (0.5-0.6) 1.3 (1.2-1.5)

Placenta accreta 0.2 (0.2-0.2) 0.2 (0.2-0.2) 0.4 (0.3-0.4)

Placental abruption 1.4 (1.4-1.5) 1.3 (1.3-1.4) 1.8 (1.6-1.9)

Birth outcomes

Spontaneous PTB 4.0 (3.9-4.1) 3.8 (3.7-3.9) 4.6 (4.4-4.9) <0.001

Iatrogenic PTB 2.8 (2.7-2.8) 2.5 (2.5-2.6) 3.6 (3.4-3.9) <0.001

Gestational age (weeks), mean (SD) 38.8 (1.8) 38.9 (1.8) 38.6 (1.9) <0.001

Low birthweight 5.3 (5.1-5.4) 5.0 (4.8-5.1) 6.5 (6.2-6.8) <0.001

Birthweight (g), mean (SD) 3329 (538) 3340 (532) 3285 (562) <0.001

Parity and past PTB < 37 weeks

Primiparous 41.2 (40.9-41.4) 44.9 (44.6-45.2) 25.5 (25.0-26.0) <0.001

Multiparous and no past PTB 53.2 (52.9-53.4) 50.0 (49.8-50.3) 66.5 (65.9-67.0)

Multiparous and past PTB 5.6 (5.5-5.8) 5.1 (5.0-5.2) 8.0 (7.7-8.3)

Maternal comorbidity scorea

0 80.8 (80.6-81.0) 83.1 (82.8-83.3) 71.3 (70.8-71.8) <0.001

≥1 19.2 (19.0-19.4) 16.9 (16.7-17.2) 28.7 (28.2-29.2)

Mode of delivery and maternal LOS

Spontaneous vaginal 59.5 (59.2-59.7) 61.4 (61.1-61.7) 51.4 (50.8-52.0) <0.001

Prolonged LOS (>2 days) 9.0 (8.8-9.2) 8.9 (8.7-9.1) 9.3 (8.8-9.8) 0.150

Operative vaginalb 11.4 (11.2-11.6) 11.8 (11.6-12.0) 9.7 (9.4-10.1)

Prolonged LOS (>2 days) 19.0 (18.3-19.5) 18.9 (18.3-19.6) 19.1 (17.7-20.6) 0.803

Cesarean section 29.1 (28.9-29.4) 26.8 (26.6-27.1) 38.9 (38.3-39.5)

Prolonged LOS (>4 days) 6.5 (6.2-6.7) 6.2 (5.9-6.5) 7.2 (6.8-7.7) <0.001

Abbreviations: LOS, length of stay at delivery hospitalization in days from date of admission to date of discharge; PTB, preterm birth. Prolonged LOS
was derived from population norms for average LOS in Canada (Metcalfe et al, 2016, http://doi:10.1136/bmjop en-2016-012007).
aMaternal comorbidity scores were measured using the obstetric comorbidity index.20,21
bOperative vaginal included forceps- or vacuum-assisted delivery.

464  |     SCIME Et al.

the nature of this difference in risk varied according to advanced
maternal age cut-point. Overall, pregnancy complications were
strongly and significantly associated with risk of PTB, with placental
disorders and preeclampsia conferring the highest risk. PAFs of both
sPTB and iPTB were consistently higher among older women, and
these age differences were statistically significant for preeclamp-
sia and placental disorders but not gestational diabetes. Placental
disorders contributed to approximately 1 in 8 sPTB among women
aged ≥35 years vs 1 in 12 sPTB among women aged <35 years, and
preeclampsia contributed to nearly 1 in 5 iPTB among women aged
≥35 years vs 1 in 7 iPTB among women aged <35 years.

Our research provides the novel contribution of quantifying
age modification of the association between pregnancy complica-
tions and PTB, which has rarely been examined in previous stud-
ies. Findings indicate that, among women with gestational diabetes,
advanced maternal age itself does not appear to elevate the risk of
sPTB or iPTB beyond what is expected in younger women. This in-
formation may improve risk estimation and communication about
PTB, if included with other known risk factors (eg, parity, lifestyle).
Qualitative studies with older mothers indicate that such informa-
tion and reassurance from clinicians help to offset concerns about
perinatal health, and more appropriately frame personal perceptions
of risk.24

Results suggest that the risks of sPTB and iPTB from preeclamp-
sia could be partly dependent on maternal age. In our study, the
aRDs for both PTB types given a preeclampsia diagnosis were higher
among older women, with an excess risk of approximately 4% for
sPTB (9.9% vs 6.1%) and 9% for iPTB (29.5% vs. 20.8%). Our alterna-
tive analyses supported the presence of modest positive age modifi-
cation for preeclampsia and sPTB (RERI 0.6, 95% CI −0.1 to 1.2) and
iPTB (RERI 1.8, 95% CI 0.3-3.2); however, only the latter value was
statistically significant. Our findings are somewhat consistent with
one previous Finnish study indicating that advanced maternal age is
a risk factor for PTB among primiparous women with preeclampsia,25
in which the analysis was restricted to affected women (age as the

exposure). This differed from our approach of analyzing the entire
population, using PTB types, and stratifying by age. Taken together,
maternal age appears to potentiate the risk of PTB associated with
preeclampsia, with stronger effect modification occurring for iPTB
than for sPTB. For sPTB, the magnitude of age modification may be
small but aligns with biological sciences research on aging-related
impairments in reproductive functioning. For example, analyses of
both human and rodent data suggest that advanced maternal age
is associated with uterine dysfunction (eg, reduced decidualization)
and altered utero-placental vascular function (eg, enhanced myo-
genic response), even when samples are restricted to pregnancies
with normal outcomes.26-28 Consequently, older mothers may expe-
rience more severe physiologic responses to the incomplete spiral
artery remodeling, imbalance of angiogenic factors, oxidative stress,
and inflammation that characterizes preeclampsia,29 possibly wors-
ening ischemia and/or triggering sPTB.30 Further research on the po-
tential mechanisms for age modification of the preeclampsia-sPTB
relation would be valuable. For iPTB, care-related mechanisms could
involve a cascade of interventions or different treatment algorithms
for women presenting with both older age and a preeclampsia
diagnosis.

Other observed age-related differences in risk of PTB are less
straightforward. Although statistically significant, the additive age
modification detected in our main analysis between placental dis-
orders and iPTB (adjusted RD 14.1% for ≥35 vs RD 11.0% for <35),
with an excess risk of approximately 3% is small and may reflect
normal variation in individual clinician’s perceptions of maternal and
fetal risk. The age modification detected in our sensitivity analysis
indicating that risk of iPTB from placental disorders is in fact higher
among women aged <40 years (aRR 5.6) than women aged ≥40 years
(RR 3.4) may be due to the higher underlying (unexposed) risk for
PTB in older women and the underestimated risk among those ex-
posed (given the absence of stillbirth data). Future studies includ-
ing all births would help to clarify the role of maternal age in this
scenario.

T A B L E 2   Prevalence of singleton live birth PTB at <37 weeks among women exposed and unexposed to pregnancy complications
stratified by maternal age

Pregnancy complication

Spontaneous PTB Iatrogenic PTB

Overall
n (%)

<35 years
n (%)

≥35 years
n (%)

Overall
n (%)

<35 years
n (%)

≥35 years
n (%)

Preeclampsia

Exposed 322 (11.6) 217 (10.3) 105 (15.5) 718 (25.9) 492 (23.5) 226 (33.4)

Unexposed 5726 (3.8) 4487 (3.7) 1239 (4.3) 3474 (2.3) 2636 (2.2) 838 (2.9)

Gestational diabetes

Exposed 592 (5.3) 359 (5.0) 233 (5.9) 538 (4.8) 326 (4.5) 212 (5.4)

Unexposed 5456 (3.9) 4345 (3.7) 1111 (4.4) 3654 (2.6) 2802 (2.4) 852 (3.4)

Placental disorders

Exposed 720 (20.6) 508 (20.3) 212 (21.5) 516 (14.8) 341 (13.6) 175 (17.7)

Unexposed 5328 (3.6) 4196 (3.5) 1132 (4.0) 3676 (2.5) 2787 (2.3) 889 (3.2)

Abbreviation: PTB, preterm birth.

     |  465SCIME Et al.

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, p
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466  |     SCIME Et al.

Our findings support that pregnancy complications are inde-
pendent risk factors for singleton sPTB and iPTB, and have a larger
main effect on risk of PTB than advanced maternal age. Our ratio
estimates align with those reported in large, contemporary studies
ranging from approximately 2-7 for preeclampsia,12,31 4-11 for pla-
cental disorders,11 and 1-2 for gestational diabetes depending on
whether any PTB or PTB types were used.13,32,33 Several Doppler
and histological studies have characterized how preeclampsia and
placental disorders lead to sPTB, implicating a common pathophys-
iology of the placenta.34 However, biologically plausible pathways
from gestational diabetes to sPTB have yet to be described. For all
pregnancy complications, heightened concern for maternal and fetal
well-being and clinical protocols for managing high-risk pregnancy
are likely contributors to iPTB.35

In addition to quantifying individual risks, our estimation of PAFs
provides a population-level perspective to understanding how com-
plications contribute to PTB across clinically relevant maternal age
groups. In theory, PAFs represent the proportion of PTBs that would
be eliminated if the studied risk factor were eliminated.36 Our pop-
ulation-based findings are therefore useful for modifiable factors
and can inform targeted policy action, public health intervention, or
research. We observed PAFs for sPTB and iPTB that were consis-
tently and often significantly larger among older mothers regardless
of trends in aRRs across age groups, a finding that aligns with our
hypothesis. For example, with iPTB the aRR for placental disorders
was higher among women aged <35 (5.4) than women aged ≥35 (5.1),
yet the PAF was higher among women aged ≥35 (13.2%) vs women
aged <35 (8.9%). This is because PAFs contextualize risk estimates
with the proportion of PTBs exposed to complications, which we
have shown are consistently higher among older women.

Few studies have reported PAFs for pregnancy complications
and PTB, as the predominant focus has been on behavioral fac-
tors (eg, substance use).37 Comparisons to previous research are
hindered by study variation. A Canadian study reported a PAF of
1.91% for gestational diabetes, which is marginally smaller than
the PAFs of 2.0% for sPTB and 4.9% for iPTB reported in our
study.33 However, their population included multiple gestations
and stillbirths and likely has a different distribution of maternal
and obstetric characteristics compared with our sample of single-
ton live births. A US study of singleton live births reported PAFs
of iPTB of 19.1% for preeclampsia, 10.5% for placental abruption,
and 4.8% for placenta previa,12 which are somewhat similar to our
findings (approximately 14%-19% for preeclampsia and 8%-13% for
placental disorders depending on maternal age group), but the au-
thors defined PTB as <35 weeks compared with our definition of
<37 weeks. Although our estimates appear to align with published
PAF patterns, these examples highlight that careful attention to
population composition and outcome definitions is warranted
when comparing PAFs.

The presence of preeclampsia and placental disorders contrib-
uted to a significantly higher proportion of sPTB and iPTB in women
aged ≥35 years compared with women aged <35 years. Research
and policy aimed at identifying and preventing these conditions, T

A
B

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4
 

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f p

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2

(2
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%
(9

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C

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4
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)

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8

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)
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7

2.
0

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)
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3
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6

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12
1

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e

xp
os

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15

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11
.9

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16
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12

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PA
F

%
(9

5%
C

I)
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(7

.9
-9

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)

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(1
0.

6-
14

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)

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.0

01
9.

6
(8

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3)

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1.

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ot

e:
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-v
al

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s

w
er

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co

m
pu

te
d

us
in

g
Z-

te
st

s
to

c
om

pa
re

t
he

a
ge

-s
tr

at
if

ie
d

PA
Fs

.
A

bb
re

vi
at

io
ns

: P
A

F,
p

op
ul

at
io

n
at

tr
ib

ut
ab

le
f

ra
ct

io
n;

P
TB

, p
re

te
rm

b
ir

th
.

     |  467SCIME Et al.

particularly in older women, could meaningfully reduce the popu-
lation burden of PTB given the moderate size of these PAFs. PTB
is heterogeneous and multiple causative factors may be influencing
pregnancy outcome alongside complications.38 Future research ex-
ploring PAFs for combinations of medical, lifestyle, and social factors
across maternal age groups may yield valuable information given the
advent of precision public health in PTB prevention.

Our use of the DAD as a data source presents both limitations
and strengths. Non-differential misclassification bias from under-re-
porting of pregnancy complications in the DAD may have occurred.
Validation studies indicate that pregnancy complications are gen-
erally under-estimated when using delivery records compared with
multiple healthcare contacts.39 The inability to include stillbirths
in our sample likely introduced some selection bias, leading to an
under-estimated risk of PTB in exposed groups. This bias would be
more pronounced in the advanced maternal age group, because
stillbirth occurs more frequently in women aged ≥35 years.4 Some
degree of unmeasured confounding is expected given that the DAD
poorly captures assisted reproductive technology and lacks qual-
ity data on non-medical factors that influence perinatal health. Our
sensitivity analysis of e-values provides some reassurance that our
findings related to preeclampsia and placental disorders (but not
gestational diabetes) are unlikely to be fully explained by unmea-
sured confounding, because the minimum strength of association
(RRs ranging from 4 to 17) that would nullify the observed associ-
ation is implausible. Notwithstanding these limitations, use of the
DAD enabled us to capture all in-hospital deliveries in the prov-
ince. Few women were excluded for poor data quality. Our large
sample size allowed for high precision and power to detect effect
modification, reducing the likelihood of type II error and improving
generalizability.

5   |   C O N C L U S I O N

The risks of sPTB and iPTB associated with preeclampsia are sig-
nificantly higher among older mothers, which may prove useful
when estimating and communicating obstetric risk for older women.
Maternal age does not appear to meaningfully modify the risk of PTB
associated with gestational diabetes or placental disorders; however,
additional research on age modification in the context of placental
disorders is warranted. Pregnancy complications contribute to a siz-
able proportion of live PTBs in Alberta, particularly iPTBs, and are
attributable to a higher proportion of PTBs among older compared
with younger women. Our findings may be used to inform clinical
risk assessment and public health policy pertaining to PTB.

A C K N O W L E D G E M E N T S
We thank Stephanie Garies and Bing Li for their assistance in obtain-
ing and managing this dataset.

C O N F L I C T O F I N T E R E S T
None.

O R C I D
Natalie V. Scime https://orcid.org/0000-0002-5811-7661

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S U P P O R T I N G I N F O R M AT I O N
Additional supporting information may be found online in the
Supporting Information section.

How to cite this article: Scime NV, Chaput KH, Faris PD, Quan
H, Tough SC, Metcalfe A. Pregnancy complications and risk of
preterm birth according to maternal age: A population-based
study of delivery hospitalizations in Alberta. Acta Obstet
Gynecol Scand. 2020;99:459–468. https ://doi.org/10.1111/
aogs.13769