Perinatal health outcomes of offspring of internal migrant women according to human development index: a registry-based cohort study of over 10 million live births from Brazil.

Background: Migration, driven by factors like poverty, violence, and natural disasters, is a key social determinant of health. While international migrants often have worse perinatal outcomes, research on perinatal health differences between internal migrants and non-migrants remains limited. We aimed to determine whether the offspring of women who migrate within Brazil experience poorer perinatal outcomes than those of non-migrants, according to the Human Development Index (HDI) of their municipalities of origin and destination. Methods: We used the CIDACS Birth Cohort, consisting of women applying for social programmes in the Unified Registry for Social Programmes Findings: We included 10,184,021 births in the study, with 5.7% of these births from women who were internal migrants. The offspring of women who migrated to municipalities with equal/higher HDI (80% of migrations), exhibited a decreased risk of preterm births (RR: 0.94, 95% CI: 0.93-0.95), low birth weight (RR: 0.94, 95% CI: 0.92-0.95) and small for gestational age (RR: 0.92, 95% CI: 0.91-0.93), but higher risk of congenital abnormalities (RR: 1.14, 95% CI: 1.10-1.18). The offspring of women who migrated to municipalities with lower HDI had delayed access to healthcare and worse outcomes except for a lower risk of low birth weight (RR: 0.94, 95% CI: 0.92-0.96). Interpretation: Offspring of those migrating to municipalities with equal/higher HDI tend to have better perinatal outcomes, whereas migrants to lower HDIs have a similar pattern to non-migrant women. Funding: NIHR, Wellcome Trust, Royal Society.