Relationship between Extra-long Interpregnancy Interval and Adverse Perinatal Outcomes in Chinese Women

Background: Since China implemented the one-child policy in September 1980 to the full opening of the two-child policy in January 2016, the 35 year one-child policy has made many women choose to have a second child after many years, resulting in a group of women with extra-long interpregnancy interval (IPI). Objective: To investigate the association between extra-long interpregnancy interval and adverse perinatal outcomes stratified by maternal age at childbearing in the index pregnancy. Methods: A retrospective cohort study on women experiencing their second delivery between 2017 and 2018 in a maternal and child health hospital was conducted. Maternal age at delivery was divided into women aged 20–34 years, women aged 35–39 years and women aged 40 and older. Interpregnancy interval (IPI) was defined as the interval between the date of a live birth and the start of the subsequent pregnancy. IPI ≥180 months was defined as extra-long IPI. Logistic regression analysis was performed to explore the adverse perinatal outcomes in different IPI groups, and compared with the predicted risks at 24–59, 60–119, 120–179, and 180-month IPI, with the 12–23-month interval serving as a reference. Results: After adjusting for age, occupation, marital status, educational level, multiple abortion history (3 times or more), history of spontaneous abortion and history of cesarean section, the rate of gestational diabetes mellitus increased with increasing IPI in all maternity groups, among them IPI 120-179 months (aRRs 1.52, 95% CI 1.10–2.10) and IPI ≥ 180 months (aRRs 1.58, 95% CI 1.06–2.34), but this phenomenon does not exist after stratification by age. With regard to premature rupture of membrane, an increased risk was reported for mothers with IPI of 24–59 months (aRRs 1.44, 95% CI 1.01–2.06), IPI of 60-119 months (aRRs 1.47, 95% CI 1.00–2.15), IPI of 120–179 months (aRRs 1.70, 95% CI 1.12–2.58), and IPI ≥ 180 months (aRRs 2.08, 95% CI 1.27–3.40) in all maternity groups. And an increased risk of premature rupture of membrane was reported for mothers with IPI of 60–119 months (aRRs 1.83, 95% CI 1.13–2.97) and IPI of 120–179 months (aRRs 3.30, 95% CI 1.40–7.74) in women aged 20-34. However, the effects of extra-long IPI on adverse perinatal outcomes did not significantly differ among women aged 35 years or older. Conclusions: These results indicate that long IPI (60–179 month) is an independent risk factor for premature rupture of membranes. Extra-long IPI (≥180 months) was not associated with an increase in major morbidity, but extra-long IPI often coexists with advanced age, so we still need to pay attention to the maternal risk factors associated with extra-long IPI.