Impact of Air Pollution Reductions during the Beijing Olympics on Pre-term birth

描述（由研究者提供）：最近的研究提供了一些证据，表明空气污染与不良出生结局（包括早产和胎儿生长受限）之间存在关联。然而，这些研究在与不良出生结局最一致的污染物和怀孕期间污染物浓度与这些不良结局相关的时间窗方面都不一致。审查建议使用“自然实验”，即对一个城市或地区空气污染的巨大和剧烈变化进行研究，以便对健康结果与环境空气污染水平之间的任何关系进行更有控制的评估。我们建议在2008年夏季奥运会期间利用北京的自然实验，在6周的时间里，空气污染水平急剧下降，然后在奥运会结束后恢复到接近奥运会前的水平。我们将研究这些污染物的减少是否与早产率的降低和出生体重的增加有关。这种污染物水平降低的短时间窗口将使我们能够比以前的研究中分离出更短的怀孕期，以便更严格地评估胎儿可能易受空气污染影响的潜在怀孕期。在北京市中心的一项研究中，我们的研究小组通过评估多种生物标志物的污染相关变化，研究了空气污染对心肺健康影响的几种假设机制。在本研究中，基于相同的自然实验，我们测量了PM2.5的环境浓度，PM2.5的化学成分包括离子（如硫酸盐、硝酸盐和铵）、元素碳、有机碳、24种元素（主要是金属）、14种多环芳烃和几种气态污染物，在奥运会之前、期间和之后。我们观察到，污染物浓度从奥运会前到奥运会期间下降了31% - 59%（例如，PM2.5均值从104克/立方米下降到65克/立方米），奥运会后上升了19% - 190%。我们建议使用这些相同的污染物数据，以及在北京多个站点测量的PM10、NO2和SO2浓度，以及北京5个相邻地区3年的出生登记数据。我们将检验2008年奥运会期间与2007年同期相比，早产率和平均足月出生体重是否有显著变化。我们将估计早产的风险和足月出生体重的变化与整个怀孕期间污染物浓度的变化有关。由于采用“自然实验”设计，提出的分析更好地控制了混淆，将改善我们对污染可能对围产期健康产生影响的怀孕时间的有限理解，并将首次探索特定的PM成分是否可能导致这些不良出生结果的关联。这些发现应该有助于制定减少这些风险的公共卫生战略。

DESCRIPTION (provided by investigator): 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. PUBLIC HEALTH RELEVANCE: 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.