Effect of Interpregnancy Interval on Adverse Perinatal Outcomes in Southern China: A Retrospective Cohort Study, 2000-2015.

BACKGROUND: In January 2016, a universal two-child policy was introduced in China. The association of interpregnancy interval (IPI) with perinatal outcomes has not previously been assessed among Chinese population. We investigated the effect of IPI after live birth on the risks of preterm delivery, and small, and large for gestational age births in China.

METHODS: We conducted a cohort study among 227 352 Chinese women with their first and second delivery during 2000 to 2015. IPI was calculated as months from first live delivery to conception of the second pregnancy. Poisson regression models with robust variance were fit to evaluate associations of IPI with risk of adverse perinatal outcomes, adjusted for potential confounders.

RESULTS: Compared to IPI of 24- <30 months, IPI <18 months was associated with higher risks of preterm birth (PTB) and small for gestational age (SGA). For IPI <6 months, the adjusted relative risks (RR) for PTB and SGA were 2.04 (95% confidence interval [CI] 1.83, 2.27) and 1.43 (95% CI 1.31, 1.57), respectively. Women with IPI ≥60 months had higher risks of PTB and large for gestational age (LGA). For IPI ≥120 months, the adjusted RRs for PTB and LGA were 1.67 (95% CI 1.43, 1.94) and 1.10 (95% CI 0.97, 1.26).

CONCLUSIONS: Women with IPI <18 months after live birth had higher risk of PTB and SGA, and IPI ≥60 months was associated with higher risk of PTB and LGA. These findings may provide information to Chinese couples about the appropriate interpregnancy interval for a second pregnancy.