The Impacts of Environmental Exposures on Birthweight

Abstract

Environmental exposures have long been linked to health outcomes. This dissertation focuses on one outcome in particular, birthweight, as it is predictive of health status over the life course. The birth records of Massachusetts from 2001 to 2013 serve as the study population. The first study considers particulate matter under 2.5 µm in aerodynamic diameter (PM2.5), a well-established exposure risk for health detriments and decreased birthweight. Specifically, it seeks to quantify the associations between maternal exposure to PM2.5 and birthweight at different points along the birthweight distribution. This study finds that the negative associations between fine particulate air pollution and birthweight were more severe among lighter newborns than heavier newborns, even after adjustment for potential sources of confounding. The second study narrows the focus onto chemical constituents of PM2.5. It assesses the relative toxicities of elemental carbon, organic carbon, nitrate, and sulfate on birthweight while simultaneously adjusting for total fine particulate air pollution. It finds that elemental carbon was most toxic. The third study shifts away from PM2.5 and explores surrounding greenness around the maternal residence as an exposure. It finds that increased maternal exposure to greenness was associated with birthweight and that this association is nonlinear. The fourth and final study applies a measure of neighborhood social stress and privilege as an exposure. Measures of racial and economic segregation are calculated and their associations with birthweight are assessed. It finds that higher values of these measures are positively associated with birthweight and that these relationships are modified by individual maternal race and Medicaid status. The results from this dissertation inform air pollution control policy and urban planning, and identify those who are most vulnerable to environmental exposures. Analyses with novel exposures such as surrounding greenness and neighborhood social stress and privilege show that they are potentially important determinants of health and should be considered alongside well-established environmental exposures in future work.