Health insurance expansion for migrants and maternal, perinatal, and infant health outcomes in Colombia: a national cohort study (2013–2020)

Background: During the 2010s, more than 2.8 million Venezuelans migrated to Colombia. Before 2016, migrant women had access to emergency, delivery, and postnatal care but limited access to routine prenatal services. In 2016, eligibility for subsidised health insurance was extended to vulnerable migrant women. We aimed to evaluate the effect of this policy on maternal, perinatal, and infant health outcomes across four groups: migrant enrolled (ME), migrant non-enrolled (MNE), Colombian enrolled (CE), and, Colombian non-enrolled (CNE). Methods: We conducted a national retrospective cohort study of 326,968 singleton live births to migrant mothers in Colombia (2013-2020) using administrative data. We applied difference-in-differences (DiD) models comparing migrants (ME + MNE) and Colombians (CE + CNE), and difference-in-differences-in-differences (DDD) models to estimate changes among migrant women who enrolled in subsidised insurance (ME). Outcomes included infant and maternal mortality, prenatal care utilisation, gestational age, birthweight, birth length, and 5-min Apgar score. Stratified analyses assessed heterogeneity by mother's education and regional migrant density. Findings: = 0.34 visits, 95% CI 0.10-0.57), particularly among mothers with lower educational attainment. Interpretation: In an insurance-based health system, expanding subsidised coverage increased prenatal care utilisation among migrant women but was not associated with sustained reductions in mortality. These findings highlight the role of formal integration into national health systems in improving access in contexts of large-scale migration.