Trends in preterm birth in singleton and multiple gestations in the Netherlands 2008-2015: A population-based study.

Objective: Preterm birth is the most important cause of perinatal morbidity and mortality. Over the past years several preventive measures have been studied and implemented. Preterm birth percentage in 2015 in the Netherlands was 6.9 %, according to data from the European Peristat project, reporting on perinatal health in Europe. Various preventive measures might have influenced the incidence and outcome of preterm birth. Our aim was to give an overview of the trends in preterm births for both singleton and multiple gestations in the Netherlands in order to guide future research.

Study Design: We studied a nationwide cohort including both singleton and multiple gestations without congenital anomalies between 2008 and 2015. Outcomes were total preterm birth (defined as birth before 37 weeks of gestation), spontaneous and iatrogenic preterm birth < 37 weeks, spontaneous and iatrogenic preterm birth percentages between 34-36 weeks, 32-34 weeks, 28-31 weeks and ≤ 27 weeks using a moving average technique. Trend analysis was performed using the Cochran Armitage test. Singleton and multiple gestations were analyzed separately.

Results: Our final study population comprised 1,303.786 women with a singleton and 44,951 women with a multiple pregnancy. Preterm birth < 37 weeks in singletons decreased from 5.6 % in 2008 to 5.3 % in 2015 (P < 0.0001), in both spontaneous and iatrogenic preterm birth. Preterm birth ≤ 27 weeks increased from 0.40 % to 0.45 % (P for trend <0.0001). The number of multiple gestations decreased over the years, as well as the percentage of multiples conceived through IVF/ICSI. There was an increase in total and iatrogenic preterm birth < 37 weeks from 36.7-38.2% (P < 0.0001) in multiples. The number of multiples <32 decreased, in both the spontaneous and iatrogenic group.

Conclusion: In the Netherlands preterm birth risk in singletons decreased between 2008 and 2015 but an increase was noted in preterm birth ≤ 27 weeks. In multiples the total preterm birth risk increased, due to an increase in indicated preterm birth.