Ambient Air Pollution and Preterm Birth A Time-series Analysis

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 mu m in diameter (PM10), particulate matter <2.5 mu m in diameter (PM2.5), and speciated PM measurements. Daily pollutant levels in 5-country 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 PM2.5 sulfate and PM2.5 water-soluble metal concentrations in the preceding week. Conclusions: Results provide limited support for late-pregnancy effects of ambient air pollution on preterm birth.