Associations between prenatal traffic-related air pollution exposure and birth weight: Modification by sex and maternal pre-pregnancy body mass index

Background: Prenatal traffic-related air pollution exposure is linked to adverse birth outcomes. However, modifying effects of maternal body mass index (BMI) and infant sex remain virtually unexplored. Objectives: We examined whether associations between prenatal air pollution and birth weight differed by sex and maternal BMI in 670 urban ethnically mixed mother-child pairs. Methods: Black carbon (BC) levels were estimated using a validated spatio-temporal land-use regression (LUR) model; fine particulate matter (PM_2.5) was estimated using a hybrid LUR model incorporating satellite-derived Aerosol Optical Depth measures. Using stratified multivariable-adjusted regression analyses, we examined whether associations between prenatal air pollution and calculated birth weight for gestational age (BWGA) z-scores varied by sex and maternal pre-pregnancy BMI. Results: Median birth weight was 3.3±0.6kg; 33% of mothers were obese (BMI ≥30kg/m³). In stratified analyses, the association between higher PM_2.5 and lower birth weight was significant in males of obese mothers (-0.42 unit of BWGA z-score change per IQR increase in PM_2.5, 95%CI: -0.79 to -0.06) ( PM_2.5×sex×obesity P_interaction=0.02). Results were similar for BC models (P_interaction=0.002). Conclusions: Associations of prenatal exposure to traffic-related air pollution and reduced birth weight were most evident in males born to obese mothers.