Taking advantage of the natural experiment of the 2008 Beijing Olympics (8/8 to 9/24), when air pollution levels decreased by 13%–60%, we assessed whether having ≥1 pregnancy month during the Olympics was associated with decreased risks of hypertensive disorders (HD) and/or fetal-placental conditions (FPC). We included singleton births to mothers with ≥1 pregnancy month in 2008 or 2009 (n=56,155). Using generalized additive models, we estimated the risk of HD and FPC associated with 1) the 2008 Olympics compared with the same dates in 2009, and 2) increased mean ambient PM10, NO2 and SO2 concentrations during each trimester. However, we found no association between HD or FPC and having any trimester during the 2008 Olympic period. This may, in part, be due to a small number of pregnancy complications in this population.
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