Limited studies have conducted a comprehensive investigation on the impact of China’s birth policy change on the mental health among women of childbearing age. This study aimed to explore the potential impact of China’s Universal two-child policy on depressive symptoms among women of childbearing age, based on national-representative, longitudinal survey data.

Data we employed in this study were derived from the China Family Panel Study (CFPS) for the waves of 2012, 2014, 2016, 2018 and 2020. We included 7481 currently married females (17079 for pooled sample) aged 20–40 years. Depressive symptoms were assessed using the Kessler 6 Rating Scale (K6) and the Center for Epidemiologic Studies Depression Scale (CES-D). All scores were standardized for analysis. We employ the difference-in-difference model to investigate the association between the implementation of the Universal Two-child Policy (UTP) and women’s depressive symptoms.

Women in the exposed group, after implementing UTP, had a standardized score of depressive symptoms 0.10 higher (95% CI: 0.03–0.16, p = 0.007) than during the pre-intervention period after controlling for multiple covariates. They also faced a higher risk of having moderate or severe depressive symptoms (OR = 1.45, 95% CI: 1.12–1.87, p = 0.004). The stratified analysis revealed that the negative impact of UTP on mental health was pronounced among women with advanced age, low education, medium family income, only male offspring before UTP, and no new birth after UTP.

We observed that the implementation of the UTP was associated with increased depressive symptoms among married women of childbearing age in China, with significant heterogeneity across different sociodemographic groups. Greater attention should be paid to the complex psychological conditions of women of childbearing age when adjusting fertility policies, which is crucial to prevent women from suffering poor mental health and to advance high-quality development in population health.