Early-pregnancy exposure to air pollution and stillbirth in São Paulo, Brazil – results from the FetRisks case-control study
Stillbirth remains a major public health concern, particularly in urban settings with persistent air pollution, while evidence remains limited in middle-income countries. This study aims to examine the association between prenatal exposure to fine particulate matter (PM2.5) PM2.5 and stillbirth in São Paulo, Brazil. Case-control study including 348 antepartum stillbirths and 419 live births recruited from 14 public hospitals. PM2.5 exposure was estimated using residential addresses linked to the nearest air quality monitoring station. We evaluated median PM2.5 levels during the first trimester of pregnancy and sustained higher PM2.5 exposure episodes (> 12.7 µg/m³ for ≥ 3 weeks). We explored the interaction between air pollution and maternal factors. Multiple logistic regression models were adjusted for maternal sociodemographics. All participants were exposed to PM2.5 concentrations substantially above the WHO Air Quality Guidelines. Sustained higher PM2.5 exposure was associated with higher odds of stillbirth (ORadj 1.51; 95% CI: 1.03–2.25) and showed a significant interaction with maternal age ≥ 35 years, increasing the odds of having a stillbirth (ratio of ORadj 2.55 [95% CI: 1.08–6.23]). Stillbirth was associated with episodes of sustained higher PM2.5 exposure in early pregnancy, in a context where all women experienced high pollutant levels. The coexistence of high baseline PM2.5 exposure and multiple maternal vulnerabilities underscore the need for integrated strategies addressing air quality, health equity, and perinatal care to reduce preventable stillbirths in highly polluted urban environments. Sustained higher PM2.5 exposure in early pregnancy increased stillbirth risk in São Paulo. All participants were exposed to PM2.5 levels above the WHO AQG 2021. Air pollution’s effect on stillbirth was higher among women with advanced age. Findings support urgent air quality improvements and integrated maternal–environmental health policies.