Ambient Air Pollution and Preterm Birth

Abstract

Background: An emerging body of evidence suggests that ambient levels of air pollution during pregnancy are associated with preterm birth. Methods: To further investigate these relationships we used vital record data to construct a retrospective cohort of 476,489 births occurring between 1994 and 2004 in 5 central counties of metropolitan Atlanta. Using a time-series approach, we examined aggregated daily counts of preterm birth in relation to ambient levels of carbon monoxide, nitrogen dioxide, sulfur dioxide, ozone, particulate matter 10), particulate matter 2.5), and speciated PM measurements. Daily pollutant levels in 5-county Atlanta were characterized using a population-weighted spatial average of air quality monitors in the study area. We also examined ambient concentrations at individual monitors in analyses limited to mothers with residential geocodes within 4 miles of each monitor. Relationships between average pollution levels during 3 gestational windows of interest were modeled using Poisson generalized linear models. Results were adjusted for seasonal and long-term time trends. Results: Although most results were null, there were 3 positive associations between ambient pollution levels and preterm birth in the 4-mile capture-area analyses. Daily preterm birth rates were associated with average NO₂ concentrations in the preceding 6 weeks and with average PM_2.5 sulfate and PM_2.5 water-soluble metal concentrations in the preceding week. Conclusions: Results provide limited support for late-pregnancy effects of ambient air pollution on preterm birth.