Impact of evolving fertility policies on maternal and neonatal outcomes in southeastern China: a 10-year population-based cohort study

BACKGROUND: After over three decades of the one-child policy (OCP), China introduced the partial two-child policy (PTCP) in 2013 and the universal two-child policy (UTCP) in 2015. However, their potential impacts on maternal and neonatal health remain unclear. This study aimed to examine temporal changes in maternal characteristics and neonatal outcomes across different policy periods. METHODS: We used data from a population-based pregnancy registry in Ximen, China. Maternal characteristics and neonatal outcomes were compared across the three periods: OCP (2012-2014), PTCP (2014-2016), and UTCP (2016-2021). Joinpoint regression and interrupted time series (ITS) model were applied to evaluate temporal trends and quantify the effect of policy implementation on trends over time. RESULTS: Among 491 895 pregnancies, the proportion of advanced maternal age and multiparity rose significantly after policy shifts. Maternal obesity, hypertensive disorders of pregnancy, and gestational diabetes showed steady increases. Monthly births peaked in 2016, then declined below the pre-PTCP baseline level by 2020. Compared to OCP, the prevalence of birth defects (BDs) increased by 62% during PTCP and 204% during UTCP. Preterm birth and low Apgar scores also rose. ITS indicated a significant post-UTCP acceleration in BDs (β3 = 2.57), largely driven by circulatory system BDs, with maternal age acting as a partial mediator. CONCLUSION: China's TCP implementation was associated with notable shifts in maternal risk profiles and increased adverse neonatal outcomes, underscoring the need for continuous maternal-child health monitoring during fertility policy transitions.