Prenatal ambient air pollution exposure and small for gestational age birth in the Puget Sound Air Basin

Several studies have identified high concentrations of air pollution as harmful to the developing fetus, but few studies of traffic-derived air pollution and birth outcomes have been conducted in areas of low to moderate air pollution. We identified singleton live births between 1997 and 2005 (N = 367,046 births) in the Puget Sound Air Basin of Washington State. We estimated nitrogen dioxide (NO2) exposure using a land use regression model of traffic, PM2.5 exposure from the nearest community monitor, and proximity to highways/roadways for the residential location of all subjects. Logistic regression estimates of odds ratios (OR) of small for gestational age (SGA) and low birth weight (<2,500 g) among term births were calculated. We observed a modest association between SGA births with increasing quartile of first trimester NO2 exposure: second (OR = 1.01, 95 % confidence interval (CI) 0.97, 1.04), third (OR = 1.06, 95 % CI 1.03, 1.10), and fourth (OR = 1.08, 95 % CI 1.04, 1.12) (p trend <0.001). We did not observe an association between PM2.5 and SGA or low birth weight among term births. Our findings suggest that prenatal exposure to traffic-derived air pollutants has a modest effect on fetal growth in a region with low overall air pollutant concentrations. Given the modest associations, future studies in similar settings that maximize the opportunity to address potential residual confounding are needed.