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

INTRODUCTION

Ozone (O) 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 O exposure among 655,529 pregnancies with conception dates between 2005 and 2007. Individual O 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 O (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 O (OR=1.04, 95% CI: 1.03, 1.06; OR=1.03, 95% CI: 1.02, 1.04; OR=1.07, 95% CI: 1.05, 1.08). In the distributed lag models, elevated odds of HDP were observed with increased O exposure during the 1st to 24th weeks of gestation, with higher odds during early pregnancy.

CONCLUSIONS

O exposure during pregnancy is related to increased odds of HDP, and early pregnancy appears to be a potentially critical window of exposure.