Ozone exposure and the risk of gestational hypertension in a northern Chinese city: Identifying the critical windows of exposure.

Increasing evidence indicates the potential association between maternal exposure to air pollution and adverse obstetric outcomes. However, the relationship between ozone (O3) and hypertensive disorders of pregnancy (HDPs) is limited and inconsistent. Therefore, it is necessary to clarify the role of O3 in the risk of HDPs, particularly across diverse geographic and demographic groups. This cohort study included a total of 28,908 pairs of mothers and infants in a northern Chinese city, a typical energy production base, between January 2018 and December 2020. To screen for gestational hypertension (GH, a typical type of HDPs), data on blood pressure after 20 weeks of gestation were collected from electronic birth records. The trimester- and weekly-specific associations between O3 and GH were assessed using logistic regression and distributed lag non-linear models (DLNMs), respectively. Odds ratios (ORs) with 95% confidence intervals (CIs) were also calculated. The average exposure levels of O3 during the preconception, first trimester, second trimester and 1st+2nd trimesters were 99.5, 100.8, 101.6, and 101.1 μg/m3, respectively. At trimester levels, O3 was positively associated with GH in the preconception period (OR = 1.290, 95% CI: 1.193-1.394), first trimester (OR = 1.151, 95% CI: 1.064-1.245), second trimester (OR = 1.126, 95% CI: 1.047-1.211), and 1st+2nd trimesters (OR = 1.340, 95% CI: 1.190-1.509). At weekly levels, O3 was positively associated with GH at 10 to 9 weeks before pregnancy and 6 weeks before pregnancy to 6 weeks of gestation. The strongest correlation was observed in the first week of gestation (OR = 1.074, 95% CI: 1.049-1.100). The findings provide solid epidemiological evidence for developing effective air pollution control policies and optimizing preconception and prenatal care.