Ozone and hypertensive disorders of pregnancy in Florida: Identifying critical windows of exposure

Abstract

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 (OR_Trimester1=1.04, 95% CI: 1.03, 1.06; OR_Trimester2=1.03, 95% CI: 1.02, 1.04; OR_Trimester1&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.

Keywords: Air pollution; Hypertensive disorders of pregnancy; Ozone; Windows of exposure.