Association Between Interpregnancy Interval and Adverse Neonatal and Maternal Outcomes Stratified by Gestational Age in Previous Pregnancy in China

Background: With the increasing need to explore the association between interpregnancy interval (IPI) and adverse maternal and neonatal outcome, numerous studies have been conducted worldwide. However, national reports of the IPI in China are lacking. Furthermore, except for age as a known factor for IPI and adverse maternal and neonatal outcomes, the effect of gestational age in previous pregnancy is unknown. The aim of this study was to determine the IPI distribution between 2010 and 2019 and identify the effect of IPI and gestational age in previous pregnancy on adverse maternal and neonatal outcomes in China.  Methods: We used individual data from China's National Maternal Near Miss Surveillance System (NMNMSS) between 2010 and 2019. The surveillance system collected data prospectively on all pregnant and postpartum women admitted to the obstetric department. The analysis was restricted to women with records of at least two consecutive singleton births and without any complication that the NMNMSS collected during their previous pregnancy. Multivariable generalized linear models with the restricted cubic spline (RCS) were used to evaluate the effect of IPI on each adverse neonatal and maternal outcome on different categories of gestational age in previous pregnancy. Further analysis was performed in subgroups categorized by the gestational age of previous pregnancy.  Results: Over the study period, 408,843 women with 420,810 pregnancies were enrolled in our study. The median and quartile range of IPI was 32 [22, 47] months. Few women (49,084, 11.67%) became pregnant again within an extremely short (≤6 months) or long (≥60 months) IPI, and over half (289,846, 68.88%) of the women became pregnant again after an IPI between 7 and 42 months. The risk of large for gestational age (LGA), Gestational Diabetes Mellitus (GDM) and gestational hypertension was increased with increased IPI, while the risk of spontaneous preterm and small for gestational age (SGA) was inversely decreased with increased IPI. The relationship between IPI and all the other adverse neonatal and maternal outcomes was in a “U” shape. The risk of adverse neonatal and maternal outcomes differs between subgroups stratified by gestational age in the previous pregnancy. The risk of spontaneous preterm and abortion at short IPI, iatrogenic preterm, GDM, preeclampsia or eclampsia and gestational hypertension at long IPI increased more when women were of a greater gestational age in the previous pregnancy.  Conclusions: This was the first comprehensive exploration of the IPIs of Chinese women from a national database. In this research, both extreme short and long IPI were associated with a higher risk of adverse maternal and neonatal outcomes. The gestational age in the previous pregnancy was also a determinant factor for the adverse maternal and neonatal outcomes in subsequent pregnancies. Funding Statement: This study was supported by the National Key R&D Program of China (Grant No. 2019YFC1005100), the National Health Commission of the People’s Republic of China, the China Medical Board (Grant No. 11-065), the WHO (Grant No. CHN-12-MCN-004888), and UNICEF (Grant No. 2016EJH016). Declaration of Interests: The authors declare no competing interests. Ethics Approval Statement: This study was approved by the ethics committee of the West China Second University Hospital.