Area-Level Socioeconomic Deprivation, Air Pollution And Term Birth Weight

Abstract

Numerous studies have linked air pollution with adverse birth outcomes, but relatively few have examined differential associations across the socioeconomic gradient. To evaluate interaction effects of gestational nitrogen dioxide (NO2) exposure and area-level socioeconomic deprivation on fetal growth, we used: used: 1) highly spatially-resolved air pollution data; and 2) spatially-stratified principle component analysis of census variables previously associated with pregnancy outcomes to define area-level deprivation. Hospital birth records for years 2008-2010 were restricted to full-term, singleton births to non-smoking mothers (n = 243,853). We used generalized additive mixed models to examine the potentially non-linear interaction of NO2 and deprivation categories on birth weight (and estimated linear associations, for comparison), adjusting for individual-level socio-demographic characteristics and co-occurring fine particulate matter (PM2.5) exposures. Estimated NO2 exposures were highest, and most varying, among mothers residing in the most affluent census tracts. We found a non-linear inverse association between NO2 and birth weight, which was most pronounced in the least deprived areas, null in the middle range of deprivation, and inverse among the most deprived areas (p-values < 0.001, 0.9, and 0.06, respectively). Likewise, in linear models, a 10 ppb increase in NO2 conferred a 16.2 g decrease (95% CI: -21.9 to -10.5) in birth weight among mothers in the least-deprived quartile, and non-significant decrements in the mid-range and most-deprived areas [β = 0.5 g (95% CI: -7.7 to 8.7) and -11.0 g (95% CI: -22.8 to 0.9), respectively]. Our results indicate complex patterning in air pollution and deprivation in relation to birth weight, and highlight the importance of considering differential distributions of air pollution concentrations, and potential differences in susceptibility, across deprivation levels.