Environmental Toxicants and Preterm Birth in Mexico City: A Geo-spatial Approach for Use in Epidemiology.

Abstract

Much previous epidemiologic research on outdoor air pollution and perinatal outcomes has combined data from birth registries which often lack information on mothers’ location during pregnancy, and concentrations of pollution measured at government-run air quality monitors. This dissertation develops and compares methods (citywide average (CWA), nearest monitor (NM), inverse distance weighting (IDW), and ordinary kriging (OK)) to assess exposure during pregnancy over both time and space among 1,000 simulated women from five zones of Mexico City in 2008. Then associations between PM10 and O3 exposure and preterm births, and whether mother’s bone lead levels modify this association, are evaluated for a cohort of pregnant women in Mexico City (1997-2004). All assessment methods yielded similar, but not identical, results for the pollutants examined. The exposure ranges produced by spatial methods were significantly greater than CWA estimates. The degree to which the metrics differed varied by zone of residence, with much greater differences for PM10 spatial metrics compared to CWA in the industrialized area of northern Mexico City. This dissertation provided no evidence of increased risk for preterm birth among women exposed to high levels of two key pollutants (PM10 and O3) in Mexico City. Third trimester exposures showed higher effect estimates regardless of exposure assessment method. Nearest monitor method produced lower effect estimates than those of the citywide average and inverse distance weighting method. Variation in the risk of preterm birth associated with these exposures was not seen by bone lead concentration. We attribute these null findings in part to challenges of individual estimation of air pollution from air monitoring data, and in part to limited sample size. Application of geostatistical methods to estimate air pollution exposure can enhance exposure contrast in epidemiologic studies when spatial location and activity patterns are gathered, thus improving power. Environmental toxicants can impact fetal development, and Mexico City’s growing population is highly exposed to air pollution and environmental lead. Further research in this population, addressing multiple environmental exposures and employing sophisticated exposure assessment approaches, can thus contribute to understanding of the causes of adverse birth outcomes and offer insights for prevention.