Associations of maternal ozone exposures during pregnancy with maternal blood pressure and risk of hypertensive disorders of pregnancy: A birth cohort study in Guangzhou, China

Although studies have assessed the associations of maternal exposure to ozone (O₃) during pregnancy with blood pressure and the risk of hypertensive disorders of pregnancy (HDP), the results were inconsistent. Furthermore, no studies have been conducted in China where the ambient O₃ concentration continuedly increased. The present study aimed to estimate the effects of maternal exposure to O₃ during pregnancy on the HDP risk, systolic blood pressure (SBP), diastolic blood pressure (DBP) and pulse pressure (PP). All participants of pregnant women were selected from the prospective birth cohort study on Prenatal Environments and Offspring Health conducted in Guangzhou, China. A spatiotemporal land-use-regression model was used to estimate individual monthly air pollution exposure from three months before pregnancy to childbirth date. Information on HDP, SBP, DBP and PP was obtained from maternal medical records. A Logistic regression model and a mixed linear model were used to estimate the associations of maternal exposure to O₃ with the risk of HDP and blood pressure (SBP, DBP and PP), respectively. We found significant associations of maternal exposure to O₃ during the third (OR = 1.31, 95%CI: 1.07, 1.60) and the second month (OR = 1.25, 95%CI: 1.02, 1.51) before pregnancy with the risk of HDP. Observed significantly positive associations of O₃ exposures with SBP, DBP and PP during the two months before pregnancy and during the early pregnancy. The peak effects of O₃ exposure on SBP, DBP and PP were respectively observed during the second month of pregnancy (β = 1.07 mmHg, 95%CI: 0.84, 1.31 mmHg), the first month before pregnancy (β = 0.40 mmHg, 95%CI: 0.21, 0.50 mmHg) and the second month of pregnancy (β = 0.78 mmHg, 95%CI: 0.59, 0.97 mmHg). Our results suggest that maternal exposure to O₃ were positively associated with blood pressure and the risk of HDP, and the period from three months before pregnancy to the first trimester might be the critical exposure window.