Nobles CJ, et al. - In order to assess the effect of ambient air pollution on hypertension in pregnancy, researchers determined criteria pollutant and volatile organic compound levels during pregnancy using Community Multiscale Air Quality models and abstracted gestational hypertension and preeclampsia diagnoses from medical records among 49,607 women with at least 2 singleton deliveries in the Eunice Kennedy Shriver National Institute of Child Health and Human Development Consecutive Pregnancies Study (2002–2010). Low to moderate air pollution levels were recorded (eg, median 41.6 ppb for ozone and 35.1 ppb for nitrogen oxides). During preconception and the first trimester, higher levels of most criteria pollutants were associated with lower preeclampsia risk, while during second-trimester, their higher levels were correlated with greater gestational hypertension risk. Conversely, volatile organic compounds showed no correlation to gestational hypertension but were consistently correlated with higher preeclampsia risk. Hence this study provides further evidence suggesting the possible influence of air pollution on the development of hypertension in pregnancy, although these relationships may be altered by differing causes of preeclampsia and gestational hypertension.