(671) Risk of recurrent preterm birth following spontaneous immature and extreme preterm birth in the Netherlands

Spontaneous preterm birth (sPTB) has proven to be an important risk factor for recurrent sPTB, yet the lower limit of gestational age of prior birth is not well defined. In this study, we assessed the risk of recurrent sPTB following immature and extreme preterm birth between 16⁺⁰ - 27⁺⁶ weeks and we assessed the relationship between the interpregnancy interval and the recurrent risk.

Study Design:

A nationwide retrospective cohort study was conducted with data from the Perinatal Registry of the Netherlands. We included nulliparous women with a singleton pregnancy that ended in a sPTB between 16⁺⁰ and 27⁺⁶ weeks of gestation between 2010-2014 and had a subsequent pregnancy in the 5 years following. Primary outcome of this study is recurrent sPTB < 37 weeks.

Results:

In total, 1011 linked pregnancies were included. The recurrent rate of sPTB < 37 weeks with prior birth between 16⁺⁰-19⁺⁶, 20⁺⁰-23⁺⁶, and 24⁺⁰-27⁺⁶ weeks was respectively 19.0%, 29.5% and 27.6%. The recurrent rate of sPTB per gestational age at prior birth is shown in figure 1. Women with sPTB between 16⁺⁰-19⁺⁶ weeks had lower odds for recurrent sPTB compared to women with sPTB between 20⁺⁰-27⁺⁶ weeks (OR 0.59 CI 0.43-0.81). Yet they still had a sPTB recurrence rate of 19.0%, which is high considering an average PTB rate of 6.9% in the Netherlands. Nearly one third (30.1%) of women with prior sPTB between 16⁺⁰-19⁺⁶ weeks suffered recurrent pregnancy loss < 24 weeks of gestation. A short interpregnancy interval of 0-3 months was associated with significantly increased odds for sPTB < 37 (OR 1.75 CI 1.95-2.57) and sPTB < 32 weeks (OR 2.28 CI 2.42-3.71).

Conclusion:

Spontaneous preterm birth between 16-28 weeks is associated with an increased risk for recurrent sPTB in the subsequent pregnancy. Patients in this group should be regarded as high risk for recurrent sPTB and be treated as such with preventive measures. A short interpregnancy interval of 0-3 months significantly increases the odds for sPTB and should be actively discouraged.