Effects of Maternal Homelessness, Supplemental Nutrition Programs, and Prenatal PM on Birthweight.

Few studies examined the impact of maternal socioeconomic status and of its combined effects with environmental exposures on birthweight. Our goal was to examine the impact of maternal homelessness (mothers ever homeless or who lived in shelters during pregnancy) and participation in the Special Supplemental Nutrition Program for Women, Infants and Children (WIC) during pregnancy in conjunction with air pollution exposure on birthweight in the Boston-based Children's HealthWatch cohort from 2007 through 2015 (n = 3366). Birthweight was obtained from electronic health records. Information on maternal homelessness and WIC participation during pregnancy were provided via a questionnaire. Prenatal fine particulate matter (PM) exposures, estimated at the subject's residential address, were calculated for each trimester. We fit linear regression models adjusting for maternal and child characteristics, seasonality, and block-group-level median household income and examined the interactions between PM and each covariate. Prenatal maternal homelessness was associated with reduced birthweight (-55.7 g, 95% CI: -97.8 g, -13.7 g), while participating in WIC was marginally associated with increased birthweight (36.1 g, 95% CI: -7.3 g, 79.4 g). Only average PM during the second trimester was marginally associated with reduced birthweight (-8.5 g, 95% CI: -19.3, 2.3) for a 1 µg/m increase in PM. The association of PM during the second trimester with reduced birthweight was stronger among non-Hispanic Black mothers and trended toward significance among immigrants and single mothers. Our study emphasizes the independent and synergistic effects of social and environmental stressors on birthweight, particularly the potentially protective effect of participating in WIC for vulnerable populations.