Recent studies have provided some evidence of an association between air pollution and adverse birth outcomes including preterm delivery and fetal growth restriction. However, these studies have been inconsistent in both the pollutant(s) most consistently associated with the adverse birth outcome, and the time windows during pregnancy when pollutant concentrations are associated with these adverse outcomes. Reviews have suggested the use of 'natural experiments', studies of large and drastic changes in air pollution in a city or region that allow a more controlled evaluation of any association between a health outcome and ambient air pollution levels. We propose to take advantage of the natural experiment in Beijing during the 2008 Summer Olympics where air pollution levels were drastically reduced for a 6 week period, and then allowed to return to near Pre-Olympic levels after the games. We will examine whether these pollutant reductions were associated with decreases in the preterm birth rate and increases in birth weight. This short time window of reduced pollutant levels will allow us to isolate smaller periods of pregnancy than possible in previous studies, in order to more critically evaluate potential pregnancy periods when the fetus may be susceptible to air pollution. In a current study in central Beijing, our group is examining several hypothesized mechanisms of air pollution cardio-respiratory health effects by assessing pollution associated changes in multiple biomarkers. For this study, based on the same natural experiment, we have measured ambient concentrations of PM2.5, chemical constituents of PM2.5 including ions (e.g. sulfate, nitrate, and ammonium), elemental carbon, organic carbon, 24 elements (mainly metals), 14 PAHs,, and several gaseous pollutants before, during, and after the Olympic period. We have observed 31 percent-59 percent declines in pollutant concentrations from before to during the Olympics (e.g. mean PM2.5 declined from 104 to 65 5g/m3) and 19 percent-190 percent increases after the Olympics. We propose to use these same pollutant data, as well as PM10, NO2, and SO2 concentrations measured across Beijing at multiple stations, and birth registry data for a 3 year period from 5 adjacent Beijing districts. We will examine whether there were significant changes in the preterm birth rate and mean term birth weight, comparing the 2008 Olympic period to the same period in 2007. We will estimate the risk of preterm birth and change in term birth weight associated with changes in pollutant concentrations throughout pregnancy. The proposed analyses, with better control of confounding due to the 'natural experiment'design, will improve our limited understanding of the pregnancy times during which pollution may exert its influence on perinatal health and will also, for the first time, explore whether specific PM constituents may be responsible for these adverse birth outcome associations. The findings should help develop public health strategies to reduce these risks.
This project will examine the reproductive health benefit of the large and drastic air pollution reductions observed during the 2008 Beijing Summer Olympics. By studying the association between preterm birth, birth weight, and changes in the concentrations of several pollutants before, during, and after the Olympic games, the project should provide a more complete picture of the pregnancy times during which pollution may exert its influence on preterm birth and birth weight, a more comprehensive understanding of the specific pollutants and sources responsible for these associations than has been possible in previous studies, and better control of confounding due to the 'natural experiment'design.