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Long-term Trends in Singleton Preterm Birth in South Australia From 1986 to 2014

Verburg, Petra, E., MSc, MD; Dekker, Gus, A., PhD, MD; Venugopal, Kamalesh, PhD; Scheil, Wendy, MBBS, MAE; Erwich, Jan Jaap H., M., PhD, MD; Mol, Ben, W., PhD, MD; Roberts, Claire, T., PhD

doi: 10.1097/AOG.0000000000002419
Contents: Original Research

OBJECTIVE: To describe long-term trends in the prevalence of preterm birth and rates of preterm birth in singleton pregnancies complicated by hypertensive disorders 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 incidence 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 incidence 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.

In South Australia, from 1986 to 2014, the preterm birth rate among singleton births increased from 5% to 7%, mostly as a result of increased iatrogenic delivery.

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.

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.

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.

© 2018 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved.