LAUSR

Introduction: Ozone (O3) has been linked to hypertensive disorders of pregnancy (HDP). However, inconsistent results have been reported, and no study has examined the critical exposure windows during pregnancy. Materials and methods: We used Florida birth vital statistics records to investigate the association between HDP and O3 exposure among 655,529 pregnancies with conception dates between 2005 and 2007. Individual O3 exposure was assessed at mothers’ home address at the time of delivery using the Hierarchical Bayesian space‐time statistical model. We examined the association during three predefined exposure windows including trimester 1, trimester 2, and trimesters 1&2, as well as in each week of the first two trimesters using distributed lag models. Results: Pregnancies with HDP had a higher mean exposure to O3 (39.07 in trimester 1, 39.02 in trimester 2, and 39.06 in trimesters 1&2, unit: ppb) than those without HDP (38.65 in trimester 1, 38.57 in trimester 2, and 38.61 in trimesters 1&2, unit: ppb). In the adjusted logistic regression model, increased odds of HDP were observed for each 5 ppb increase in O3 (ORTrimester1=1.04, 95% CI: 1.03, 1.06; ORTrimester2=1.03, 95% CI: 1.02, 1.04; ORTrimester1&2=1.07, 95% CI: 1.05, 1.08). In the distributed lag models, elevated odds of HDP were observed with increased O3 exposure during the 1st to 24th weeks of gestation, with higher odds during early pregnancy. Conclusions: O3 exposure during pregnancy is related to increased odds of HDP, and early pregnancy appears to be a potentially critical window of exposure. HighlightsO3 exposure during the first two trimesters is associated with HDP.Such associations persisted with adjustment for confounders.Distributed lag models show that early pregnancy is a critical window of exposure.