Association of prenatal exposure to ambient air pollution with adverse birth outcomes and effect modification by socioeconomic factors.

BACKGROUND: Maternal exposure to air pollution has been associated with birth outcomes; however, few studies examined biologically critical exposure windows shorter than trimesters or potential effect modifiers. OBJECTIVES: To examine associations of prenatal fine particulate matter (PM2.5), by trimester and in biologically critical windows, with birth outcomes and assess potential effect modifiers. METHODS: This study used two pregnancy cohorts (CANDLE and TIDES; N = 2099) in the ECHO PATHWAYS Consortium. PM2.5 was estimated at the maternal residence using a fine-scale spatiotemporal model, averaged over pregnancy, trimesters, and critical windows (0-2 weeks, 10-12 weeks, and last month of pregnancy). Outcomes were preterm birth (PTB, <37 completed weeks of gestation), small-for-gestational-age (SGA), and continuous birthweight. We fit multivariable adjusted linear regression models for birthweight and Poisson regression models (relative risk, RR) for PTB and SGA. Effect modification by socioeconomic factors (maternal education, household income, neighborhood deprivation) and infant sex were examined using interaction terms. RESULTS: Overall, 9% of births were PTB, 10.4% were SGA, and mean term birthweight was 3268 g (SD = 558.6). There was no association of PM2.5 concentration with PTB or SGA. Lower birthweight was associated with higher PM2.5 averaged over pregnancy (ß -114.2, 95%CI -183.2, -45.3), during second (ß -52.9, 95%CI -94.7, -11.2) and third (ß -45.5, 95%CI -85.9, -5.0) trimesters, and the month prior to delivery (ß -30.5, 95%CI -57.6, -3.3). Associations of PM2.5 with likelihood of SGA and lower birthweight were stronger among male infants (p-interaction ≤0.05) and in those with lower household income (p-interaction = 0.09). CONCLUSIONS: Findings from this multi city U.S. birth cohort study support previous reports of inverse associations of birthweight with higher PM2.5 exposure during pregnancy. Findings also suggest possible modification of this association by infant sex and household income.