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Original Research
Long-term Trends in Singleton Preterm Birth
in South Australia From 1986 to 2014
Petra E. Verburg, MSc,MD, Gus A. Dekker, PhD,MD, Kamalesh Venugopal, PhD, Wendy Scheil, MBBS,MAE,
Jan Jaap H. M. Erwich, PhD,MD, Ben W. Mol, PhD,MD, and Claire T. Roberts, PhD
OBJECTIVE: To describe long-term trends in the preva-
lence of preterm birth and rates of preterm birth in
singleton pregnancies complicated by hypertensive dis-
orders of pregnancy, small for gestational age (SGA), and
preterm prelabor rupture of membranes (PROM) in
South Australia.
METHODS: We conducted a retrospective population
study including all singleton live births in the state of
South Australia from 1986 to 2014. Long-term trends for
preterm birth, hypertensive disorders of pregnancy, SGA,
preterm PROM as well as stillbirth were assessed using
joinpoint regression analyses. Trends in maternal age,
body mass index (BMI), ethnic diversity, parity, and
smoking over time were also assessed.
RESULTS: From 1986 to 2014, with a total of 539,234
singleton births, the overall preterm birth rates increased
from 5.1% to 7.1% (P,.001) and for iatrogenic preterm
birth increased from 1.6% to 3.2% (P,.001). The inci-
dence of hypertensive disorders of pregnancy decreased
from 8.7% to 7.2%. Among pregnancies complicated by
hypertensive disorders of pregnancy, the proportion
of preterm birth increased (10.4–17.5%, P,.001). The
incidence of SGA decreased from 11.1% to 8.0%. Among
pregnancies complicated by SGA, the proportion of
preterm birth increased (2.9–5.4%, P,.001). The inci-
dence of preterm PROM increased from 1.4% to 2.2%.
Among pregnancies complicated by preterm PROM, the
proportion of preterm birth remained stable. Preterm
stillbirth rates declined (4.23–2.32%, P,.001). Maternal
age, BMI, and ethnic diversity have all increased since
1986, whereas maternal smoking has decreased.
CONCLUSION: In South Australia, the preterm birth
rate among singletons increased from 1986 to 2014 by
40%, with iatrogenic preterm birth being responsible for
80% of this increase. Incidence of hypertensive disorders
of pregnancy and SGA declined. Among pregnancies
complicated by hypertensive disorders of pregnancy and
SGA, the proportions of preterm birth increased,
indicating earlier interventions in these women. The
diagnosis of preterm PROM increased from 1% to 2%,
and greater than 80% of preterm PROM was associated
with preterm birth after 1990. Increasing iatrogenic
delivery may be attributable, in part, to changing
maternal phenotype and to altered clinicians’ behavior.
However, improvements in fetal surveillance, particularly
ultrasonography, and advanced neonatal care may
underpin perinatal clinical decision-making and the
likelihood of iatrogenic birth.
(Obstet Gynecol 2018;0:1–11)
DOI: 10.1097/AOG.0000000000002419
Preterm birth is an important cause of perinatal
morbidity and mortality worldwide.
1
Children
born both early preterm (less than 34 weeks of gesta-
tion) and late preterm (34–36 6/7 weeks of gestation)
show higher rates of morbidity and mortality than
those delivered at term.
1
Prematurity is associated
From the Robinson Research Institute, Adelaide Medical School, University of
Adelaide, Adelaide, Australia; the Department of Obstetrics and Gynaecology,
University Medical Center Groningen, University of Groningen, Groningen, the
Netherlands; and Adelaide Medical School, University of Adelaide, Adelaide,
Lyell McEwin Hospital, Elizabeth Vale, and the Epidemiology Branch, SA
Health, Adelaide, Australia.
Presented at the Perinatal Society of Australia and New Zealand (PSANZ)
Annual Congress, April 2–5, 2017, Canberra ACT, Australia.
The authors thank midwives and staff from the Pregnancy Outcome Unit and all
the hospital and home birth midwives and neonatal nurses for their passion and
effort in managing and maintaining the completeness of the registry.
Each author has indicated that he or she has met the journal’s requirements for
authorship.
Corresponding author: Claire T. Roberts, PhD, Robinson Research Institute,
Adelaide Medical School, University of Adelaide, Adelaide 5005 SA, Australia;
email: claire.roberts@adelaide.edu.au.
Financial Disclosure
Dr. Verburg was supported by a postgraduate scholarship from the University of
Groningen. Dr. Mol is supported by a National Health and Medical Research
Council Practitioner Fellowship (GNT1082548) and provides consultancy for
ObsEva, Geneva, Switzerland. Dr. Roberts was supported by a National Health
and Medical Research Council Senior Research Fellowship (GNT1020749) and
is currently a Lloyd Cox Professorial Fellowship University of Adelaide. The
other authors did not report any potential conflicts of interest.
© 2017 by The American College of Obstetricians and Gynecologists. Published
by Wolters Kluwer Health, Inc. All rights reserved.
ISSN: 0029-7844/18
Copyright Óby The American College of Obstetricians
and Gynecologists. Published by Wolters Kluwer Health, Inc.
Unauthorized reproduction of this article is prohibited.
VOL. 0, NO. 0, MONTH 2018 OBSTETRICS & GYNECOLOGY 1
with poorer child cognitive and neurodevelopment at
school entry.
2,3
Additionally, neonates born preterm
are at increased risk for long-term chronic disease
such as obesity, metabolic syndrome, diabetes melli-
tus type 2, and cardiovascular disease.
4
Every addi-
tional week in utero, even up until term, is associated
with improved outcomes.
5
Preterm birth rates vary between 4% and 15% in
developed countries and are stable, declining, or
increasing across time in different countries.
6–12
In
addition to these contradictory results wordwide,
there are no reports of long-term trends in Australian
women.
We aimed to describe the long-term trends in
spontaneous and iatrogenic preterm birth as well as
those in pregnancies complicated by hypertensive
disorders of pregnancy, small for gestational age
(SGA), and preterm prelabor rupture of membranes
(PROM) in South Australia from 1986 to 2014.
Population data like these are required to identify
real-world trends that will inform future randomized
trials and guidelines to improve perinatal, and poten-
tially long-term, health outcomes.
METHODS
We performed a retrospective population-based
cohort study among all singleton live births with
a gestation greater than 22 weeks and a birth weight
greater than 500 g in South Australia, Australia,
between January 1986 and December 2014 recorded
in the South Australian Perinatal Statistics Collection
maintained by the Pregnancy Outcome Unit of South
Australia Health. The South Australian Perinatal
Statistics Collection collects information regarding
the characteristics and clinical outcomes of all South
Australian births notified by hospital and home birth
midwives and neonatal nurses using a standardized
Supplementary Birth Record. The Supplementary
Birth Records are checked manually for completeness
and data discrepancies and go through a series of
automated validation procedures during data entry.
Validation studies by the South Australian Perinatal
Statistics Collection have shown that notifications of
all births in South Australia on the Supplementary
Birth Record were robust for the parameters
studied.
13
Gestational age was determined by the first day of
the last menstrual period, confirmed by first-trimester
ultrasonography when available. The database does
not indicate how gestational age was determined for
individual women. Data on antenatal ultrasonography
were recorded since 1998. Over this 17-year period,
96.8% of the women had an antenatal ultrasonogram.
Preterm birth was defined as birth before 37 weeks
of gestation and was further divided into early pre-
term birth (less than 34 weeks of gestation) and late
preterm birth (34–36 6/7 weeks of gestation). Sponta-
neous birth was defined as an onset of birth without
any obstetric intervention. Iatrogenic birth was
defined as induction of labor or cesarean delivery
without labor. Both methods of iatrogenic birth were
also analyzed separately.
The pregnancy outcomes analyzed were hyper-
tensive disorders of pregnancy, SGA, and preterm
PROM. Hypertensive disorders of pregnancy was
defined as blood pressure 140/90 mm Hg or greater
on two occasions at least 4 hours apart or 170/
110 mm Hg or greater on one occasion. The South
Australian Perinatal Statistics Collection does not
record information on proteinuria, so preeclampsia
reports could not be confirmed. Small for gestational
age was defined as a neonate born with a birth weight
below the 10th percentile of the expected birth weight
for the Australian population
14
in normotensive
pregnancies only. Preterm PROM was defined as
confirmed rupture of the amniotic sac before 37 weeks
of gestation without progression into labor within
6 hours.
Stillbirth was defined as fetal death after 22 weeks
of gestation and with a birth weight greater than 500 g.
Data on stillbirth were obtained from the South
Australian Perinatal Statistics Collection. Trends in
stillbirth rates were calculated in relation to all births
(both live and stillborn) in South Australia.
Maternal risk factors potentially contributing to
changing trends in complications included maternal
age, body mass index (BMI, calculated as weight
(kg)/[height (m)]
2
), ethnicity, parity, and smoking.
Maternal age was divided in six groups: younger than
20, 20–24, 25–29, 30–34, and 35 years old or older.
Body mass index was categorized according to stan-
dard guidelines: underweight—less than 18.5, normal
weight—18.5–24.9, overweight—25.0–29.9, obese—
30.0–39.9, and morbidly obese—40.0 or greater. Parity
was defined as nulliparous: never have given birth; or
multiparous: previously have given birth one or more
times.
Time trends were assessed using Joinpoint 4.4.0.0
regression analyses.
15,16
This is a statistical method
that divides the assessed time period in several con-
tinuous linear time periods. These line segments are
joined at several time points and called change points,
or joinpoints. Joinpoint regression analysis identifies
the best fitting piecewise continuous log-linear model.
Average annual percentage change for the line
segments, or time periods, was calculated. Average
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2Verburg et al Long-term Trends in Preterm Birth in South Australia OBSTETRICS & GYNECOLOGY
annual percentage change is a method to assess the
relative change in proportion between populations
across a time period according to the following
formula:
Average Annual Percentage Change
5Proportiontime 2 2Proportiontime 1
Proportiontime 1 3100
Differences were considered significant when the
Pvalue was ,.05. All data preparation and descriptive
analyses were performed using IBM SPSS 23.
The study protocol was approved by the Human
Research Ethics Committee of the South Australian
Department of Health (HREC/13/SAH/97). The
South Australian Perinatal Statistics Collection data-
base does not contain any individual personal infor-
mation ensuring total confidentially of all patient
records.
RESULTS
From 1986 to 2014, there were 539,234 liveborn
singleton births recorded in the South Australian
Perinatal Statistics Collection. There were 32,770
(6.1%) singleton live preterm births (8,703 pregnan-
cies ended in early preterm birth and 24,067 in late
preterm birth; Table 1). The incidence of preterm
birth increased from 5.1% in 1986 to 7.1% in 2014
(average annual percentage change 1.2%, P,.001).
The early preterm birth rate showed a small but sig-
nificant 13.0% increase (trend: 1.5–1.7% average
annual percentage change 0.5%, P,.001), whereas
the late preterm birth rate increased from 3.7% in
1986 to 5.4% in 2014 (46% increase; average annual
percentage change 1.4%, P,.001). Overall, from 1986
to 2014, spontaneous preterm birth increased from
3.5% to 3.8% (average annual percentage change
0.3, P5.002) and iatrogenic preterm birth doubled
Table 1. Long-term Trends in Preterm Birth in Singleton Pregnancies in South Australia From 1986 to 2014
Condition n Time Period
Trend in
Proportion* (%) AAPC P
Preterm birth 32,770 1986–2014 5.1–7.1 1.2 ,.001
Spontaneous 19,570 1986–2014 3.5–3.8 0.3 .002
Iatrogenic 13,200 1986–1995 (1995–2014) 1.6–2.3 (2.3–3.2) 1.1 (1.9) ,.001 (,.001)
Preterm cesarean delivery 7,728 1986–2014 1.1–1.8 1.6 ,.001
Preterm induction of labor 5,462 1986–1999 (1999–2006)
(2006–2014)
0.5–1.2 (1.2–1.0)
(1.0–1.7)
7.2 (21.8)
(6.1)
,.001 (.420)
(,.001)
Late preterm birth 24,067 1986–2014 3.7–5.4 1.4 ,.001
Early preterm birth 8,703 1986–2014 1.5–1.7 0.5 ,.001
AAPC, average annual percent change.
* Trends in proportion presented were calculated as a proportion of all singleton live births. Fitted trends in proportion as a result of
joinpoint regression analysis are presented.
Fig. 1. Pregnancy duration in
singleton pregnancies in South
Australia, 1986–2014. Proportion
of singleton live births at each
week of gestation from 32 weeks.
Verburg. Long-term Trends in Preterm
Birth in South Australia. Obstet
Gynecol 2018.
Copyright Óby The American College of Obstetricians
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VOL. 0, NO. 0, MONTH 2018 Verburg et al Long-term Trends in Preterm Birth in South Australia 3
from 1986 to 2014 with rates of 1.6% in 1986, 2.3% in
1995, and 3.2% in 2014 (average annual percentage
change 1.1, P,.001 and average annual percentage
change 1.9, P,.001, respectively). Over this time,
there was a reduction in pregnancy duration (Fig. 1;
Appendix 1 [Appendix 1 is available online at
http://links.lww.com/AOG/B44]). The proportion of
pregnancies resulting in birth at 36 weeks of gestation
Fig. 2. Long-term trends
in complicated singleton
pregnancies in South
Australia, 1986–2014. The
histogram represents the
observed incidence of
hypertensive disorders of
pregnancy (A), small for
gestational age (B), and
preterm prelabor rupture of
membranes (C) by year of
birth. The bold line repre-
sents the significant and the
dashed line the non-
significant joinpoint fit for
the incidence. The time
segments are joined at
joinpoints indicated with
markers. Results of join-
point regression analyses
are presented for identified
time periods. *Significant
average annual percent
change (average annual
percent change).
Verburg. Long-term Trends
in Preterm Birth in South
Australia. Obstet Gynecol
2018.
Copyright Óby The American College of Obstetricians
and Gynecologists. Published by Wolters Kluwer Health, Inc.
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4Verburg et al Long-term Trends in Preterm Birth in South Australia OBSTETRICS & GYNECOLOGY
Fig. 3. Long-term trends in preterm birth in complicated singleton pregnancies in South Australia, 1986–2014. Observed and
fitted incidence of hypertensive disorders of pregnancy (A), small for gestational age (B), and preterm prelabor rupture of
membranes (PROM) (C) by year of birth. The histograms represent the observed incidence by year of birth. The bold line rep-
resents the significant and the dashed line the nonsignificant joinpoint fit for the incidence with markers indicating the joinpoints.
Fitted trend in proportions for identified time periods and Pvalues are presented in Table 2.
Verburg. Long-term Trends in Preterm Birth in South Australia. Obstet Gynecol 2018.
Copyright Óby The American College of Obstetricians
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VOL. 0, NO. 0, MONTH 2018 Verburg et al Long-term Trends in Preterm Birth in South Australia 5
increased from 2.1% in 1986–1990 to 3.1% in
2011–2014 (46.6% increase). The shift was also
noticeable at term. The proportion of pregnancies
resulting in birth at 40 weeks of gestation reduced
from 48.2% in 1986–1990 to 26.6% in 2011–2014.
The incidence of hypertensive disorders or preg-
nancy decreased from 8.7% in 1986 to 7.2% in 2014
(Fig. 2A) with a significant decrease in 1988–1992
(trend: 9.3–7.8%, average annual percentage change
24.5, P5.020), and 1996–2007 (trend: 9.0–7.0%,
average annual percentage change 22.3, P,.001).
The rate of preterm birth in pregnancies complicated
by hypertensive disorders of pregnancy has increased
from 10.4% in 1986 to 17.5% in 2014 (average annual
percentage change 1.9, P,.001; Fig. 3A; Table 2).
The proportion of spontaneous births in this group
was stable, whereas iatrogenic preterm birth showed
an increasing trend in 1986–1994 (trend: 6.8–11.3%,
average annual percentage change 6.5, P5.002)
followed by a smaller increase in 1994–2014 (trend:
11.3–14.7%, average annual percentage change 1.3,
P5.007). The proportion of cesarean deliveries per-
formed preterm for hypertensive disorders of preg-
nancy increased over the period from 1986–1992
(trend: 5.1–7.4%, average annual percentage change
6.4, P5.011). Preterm induction of labor in this sub-
group increased from 1986 to 1995 (trend: 1.5–4.5%,
average annual percentage change 13.0, P,.001) and
1995–2014 (trend: 4.5–6.8%, average annual percent-
age change 2.2, P5.021).
The incidence of SGA in normotensive pregnan-
cies decreased from 11.1% in 1986 to 8.0% in 2014
(Fig. 2B) with a significant decrease in 1997–2014
(trend: 9.3–8.0%, average annual percentage change
20.9, P,.001). The rate of preterm birth in pregnan-
cies complicated by SGA has increased from 2.9% in
Table 2. Long-term Trends in Preterm Births in Complicated Singleton Pregnancies in South Australia From
1986 to 2014
Condition n Time Period
Trend in
Proportion* (%) AAPC P
Hypertensive disorders
of pregnancy
42,776
Preterm birth 5,814 1986–2014 10.1–17.5 1.9 ,.001
Spontaneous 846 1986–2014 2.1–1.7 20.8 .220
Iatrogenic 4,968 1986–1994 (1994–2014) 6.8–11.3 (11.3–14.7) 6.5 (1.3) .002 (.007)
Preterm cesarean
delivery
2,999 1986–1992 (1992–2001)
(2001–2004)
(2004–2014)
5.1–7.4 (7.4–6.2)
(6.2–8.6)
(8.6–7.1)
6.4 (22.0) (11.9)
(22.0)
.011 (.164)
(.397) (.063)
Preterm induction
of labor
1,969 1986–1995 (1995–2014) 1.5–4.5 (4.5–6.8) 13.0 (2.2) ,.001 (.021)
Small for gestational age 50,631
Preterm birth 2,033 1986–2014 2.9–5.4 2.3 ,.001
Spontaneous 941 1986–2014 1.8–1.9 0.2 .683
Iatrogenic 1,082 1986–2007 (2007–2014) 1.3–2.3 (2.3–4.8) 2.6 (11.4) ,.001 (.002)
Preterm cesarean
delivery
663 1986–2014 0.8–1.9 3.0 ,.001
Preterm induction
of labor
419 1986–2003 (2003–2014) 0.5–0.6 (0.6–2.3) 1.7 (13.2) .239 (,.001)
Preterm prelabor rupture
of membranes
9,902
Preterm birth 7,872 1986–1988 (1988–1991)
(1991–2014)
61.8–45.7 (45.7–83.1)
(83.1–86.0)
214.0 (22.1) (0.1) .186 (.085) (.556)
Spontaneous 5,632 1986–1988 (1988–1991)
(1991–2014)
49.3–36.5 (36.5–61.6)
(61.6–58.4)
214.0 (19.0) (20.2) .263 (.196) (.433)
Iatrogenic 2,240 1986–1988 (1988–1991)
(1991–2014)
12.3–9.2 (9.2–21.6)
(21.6–27.6)
213.2 (32.7) (1.1) .350 (.070) (.004)
Preterm cesarean
delivery
847 1986–1993 (1993–2014) 4.1–9.6 (9.6–8.9) 13.1 (20.4) .006 (.616)
Preterm induction
of labor
1,393 1986–2014 8.0–21.3 3.6 ,.001
AAPC, average annual percent change.
* Trends in proportion presented were calculated as a proportion of all singleton live births. Fitted trends in proportion as a result of
joinpoint regression analysis are presented.
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6Verburg et al Long-term Trends in Preterm Birth in South Australia OBSTETRICS & GYNECOLOGY
Fig. 4. Maternal risk factors in South Australia, 1986–2014. Observed proportion of maternal age groups (A), ethnicity (B),
and body mass index (BMI) category (C) by year of birth or birth year category. BMI data are available only since 2007.
Verburg. Long-term Trends in Preterm Birth in South Australia. Obstet Gynecol 2018.
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VOL. 0, NO. 0, MONTH 2018 Verburg et al Long-term Trends in Preterm Birth in South Australia 7
1986 to 5.4% in 2014 (average annual percentage
change 2.3, P,.001; Fig. 3B; Table 2). The proportion
of spontaneous preterm birth was stable, whereas
iatrogenic preterm birth showed an increasing trend
for two time periods: 1986–2007 (trend: 1.3–2.3%,
average annual percentage change 2.6, P,.001)
followed by a greater increase in 2007–2014 (trend:
2.3–4.8%, average annual percentage change 11.4,
P5.002). The proportion of preterm cesarean delivery
in pregnancies complicated by SGA increased over
the period from 1986–2014 (trend: 0.8–1.9%, average
annual percentage change 3.0, P,.001), whereas
preterm induction of labor increased from 2003 to
2014 (trend: 0.6–2.3%, average annual percentage
change 13.2, P,.001).
The incidence of preterm PROM increased from
1.4% in 1986 to 2.2% in 2014 (Fig. 2C) with a signifi-
cant increase from 1991 to 2002 (trend 1.1–2.1%,
average annual percentage change 6.7, P,.001). The
rate of pregnancies complicated by preterm PROM
that also resulted in a preterm birth was stable
(Fig. 3C; Table 2). The proportion of spontaneous
preterm birth was stable, whereas iatrogenic preterm
birth in preterm PROM showed an increasing trend
for the time period from 1991–2014 (trend: 21.6–
27.6%, average annual percentage change 1.1,
P5.004). The proportion of preterm cesarean delivery
in pregnancies complicated by preterm PROM
increased over the period from 1986–1993 (trend:
4.1–9.6%, average annual percentage change 13.1,
P5.006), whereas preterm induction of labor
increased from 1986 to 2014 (trend: 8.0–21.3%, aver-
age annual percentage change 3.6, P,.001).
The stillbirth rates in all singleton births from
1986 to 2014 showed a significant decline (trend:
5.90–3.43%, average annual percentage change –1.92,
P,.001 [Appendix 2, available online at http://links.
lww.com/AOG/B44]). Among stillbirths, 69.9% were
preterm; this was stable throughout the study period
(P5.332). The preterm stillbirth rate declined from 4.
23% in 1986 to 2.32% in 2014 (average annual
percentage change 22.12, P,.001).
Maternal age, ethnicity, BMI, parity, and smoking
contribute to the risk of pregnancy complications.
From 1986 to 2014, maternal age increased: during
the period from 1986–1990, 33.5% of pregnant
women were older than 30 years of age, whereas,
from 2011–2014, approximately half (50.2%) of the
pregnant population was older than 30 years of age
(Fig. 4A). Also, the ethnic composition of the South
Australian pregnant population has changed from
92.2% of women being Caucasian in 1986–1990 to
76.4% in 2011–2014 (Fig. 4B). Maternal BMI was sta-
ble from 2007 to 2014: 28.7% of women had a BMI
above 30 (Fig. 4C). Overall, in the pregnant popula-
tion, parity has fluctuated, but there are no trends in
parity in those women who delivered preterm (data
not shown). In 1998, one fourth of women were smok-
ing at the first antenatal appointment and 21.6% con-
tinued to smoke throughout pregnancy; in 2014, this
had fallen to 10.1% of women who smoked at the first
antenatal appointment and 9.0% who continued to
smoke (Fig. 5).
DISCUSSION
In singleton pregnancies in South Australia from 1986
to 2014, there was a clear reduction in pregnancy
duration with a 40% increase of preterm birth (5.1–
7.1%), mainly as a result of late preterm birth. The
majority of the increase was the result of iatrogenic
delivery. Preterm birth rates in other developed coun-
tries over a similar timeframe are varied and
Fig. 5. The proportion of women
smoking at the first antenatal visit,
women who ceased smoking
before the first antenatal visit, and
women smoking in the second half
of pregnancy by year of birth.
Smoking data are available only
since 1998.
Verburg. Long-term Trends in Preterm
Birth in South Australia. Obstet Gynecol
2018.
Copyright Óby The American College of Obstetricians
and Gynecologists. Published by Wolters Kluwer Health, Inc.
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8Verburg et al Long-term Trends in Preterm Birth in South Australia OBSTETRICS & GYNECOLOGY
population-specific (4.3–14.7%).
10,12,17
Like South
Australia, Canada, Denmark, and Finland have also
seen increased iatrogenic preterm birth rates.
12
In the
United States and Canada, the incidence of hyperten-
sive disorders of pregnancy increased,
18,19
suggesting
this may contribute to increased preterm birth rates.
However, in our population, for all births at any ges-
tation, the incidence of hypertensive disorders of
pregnancy and SGA declined, whereas that of pre-
term PROM increased. For each pregnancy compli-
cation, the proportion resulting in preterm birth has
increased as a result of iatrogenic delivery.
Innovations in antenatal care since 1986 are
likely to have contributed to changing pregnancy
complication and stillbirth rates. South Australia does
not have structured preconception care. The small
number of women receiving preconception care
tends to be those attending fertility and recurrent
miscarriage clinics. However, pregnancy guidelines
have evolved in the last decade. Vaginal progester-
one to prevent spontaneous preterm birth in women
with a short cervix and previous preterm birth
20
has
been used since 2007. However, the efficacy of pro-
gesterone to prevent preterm birth and poor child
outcomes has recently come into question.
21
Toco-
lytic therapy changed from salbutamol before 1999
to nifedipine. These extend pregnancy for 2–3days
22
and are unlikely to affect the preterm birth rate. Bio-
chemical testing for preterm PROM and routine use
of antibiotics have improved outcomes.
23
Low-dose
aspirin in those at increased risk for hypertensive dis-
orders of pregnancy has increasingly been prescribed
since the mid-1990s.
24
Although third-trimester
growth scans are not routine for all women in South
Australia, detection of fetal growth restriction has sig-
nificantly increased by serial ultrasound scanning
with greater appreciation of stillbirth risk in fetal
growth-restricted fetuses.
25
Our data suggest that
iatrogenic delivery of fetal growth-restricted fetuses
may improve outcomes.
Improvements in markers of disease severity and
fetal growth permit informed decision-making on the
timing of birth and may partly explain the increase of
iatrogenic preterm birth in complicated pregnancies.
Both expectant management and induction of labor
appear to be safe approaches for suspected fetal
growth restrictions at greater than 36 6/7 weeks of
gestation,
26
but because stillbirth is known to
increase with gestation, there is a good rationale for
induction of labor after 38 weeks of gestation.
27
The
optimal timing for induction of labor for preterm
fetal growth restriction is unknown. Expectant man-
agement is preferred in pregnancies complicated by
nonsevere hypertensive disorders of pregnancy or
preterm PROM between 34 and 36 weeks of gesta-
tion in the absence of signs of infection or fetal
compromise.
5,28,29
Long-term effects of expectant
management in these pregnancy complications are
unknown.
Advanced neonatal intensive care regimes, neuro-
prophylaxis with magnesium sulphate,
30
and routine
glucocorticoid therapy before preterm induction of
labor may have alleviated clinicians’concerns about
acute neonatal morbidities associated with preterm
birth, in particular respiratory distress syndrome.
Indeed, preterm stillbirth rates in South Australia
were 4.23% in 1986 declining to 2.32% in 2014
(P,.001). It is likely that early intervention and there-
fore increased iatrogenic preterm birth has contrib-
uted to this decline.
Several other maternal and pregnancy-related
risk factors may contribute to population differ-
ences in preterm birth, including maternal age,
BMI, and ethnicity.
10,31–33
Body mass index in
women of reproductive age is increasing globally
34
and in Australia, maternal obesity increased from
5% to 19% in 1980–2013.
35,36
Currently, more than
one fourth of the South Australian pregnant popu-
lation is obese or morbidly obese. Additionally,
more than half are 30 years of age or older and
almost one fourth are non-Caucasians, both of
which increase risk. Smoking cessation is strongly
recommended to reduce preterm birth.
10
Maternal
smoking rates in South Australia have more than
halved since 1998.
Our study is limited by the data available. Some
potentially relevant factors were not collected during
the entire study period such as maternal smoking,
ultrasonography (both since 1998), and BMI (since
2007). However, the South Australian Perinatal
Statistics Collection records data on all births in South
Australia, so the data herein for 539,234 births should
be considered as a true representation of the South
Australian and Australian populations.
In singleton pregnancies in South Australia from
1986 to 2014, pregnancy duration has reduced with
both early and late preterm birth rates increasing since
1986. Overall, the proportions of iatrogenic preterm
birth in pregnancies complicated by hypertensive
disorders of pregnancy, SGA, and preterm PROM
have increased. Increasing iatrogenic delivery may be
attributable, in part, to changing maternal phenotype
and to altered clinicians’behavior. However, im-
provements in technologies to monitor pregnancy
and advanced neonatal care may underpin clinical
decision-making and reduce stillbirth risk.
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VOL. 0, NO. 0, MONTH 2018 Verburg et al Long-term Trends in Preterm Birth in South Australia 9
Randomized clinical trials to evaluate the optimal
method and timing of delivery for the growth-
restricted fetus at 34–36 weeks of gestation and studies
to determine long-term health effects of preterm inter-
ventions in the offspring are needed.
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