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Background: An estimated 17.6 million Americans live within 1.6km of an oil or gas drilling site, and this industry is rapidly expanding. Recent evidence suggests that drilling-related exposures are associated with increased blood pressure. No studies have focused on pregnant women, a population that may be highly susceptible to drilling-related air pollution (e.g. truck traffic, gas flaring.) Using a difference-in-differences design, we examine associations between drilling exposures and pregnancy-related hypertension.

Methods: We utilized a population-based retrospective term birth cohort (37-42 weeks gestation) between 1996 and 2009 in Texas, where all mothers reside <10km of an active or future drilling site (n=2,598,025). Using full address data, we linked maternal residences at delivery to the coordinates of active oil and gas extraction sites between 1985 and 2019. We evaluated two markers of pregnancy-related hypertension (gestational hypertension, eclampsia) in a difference-in-differences framework. This design first evaluates hypertension risks among pregnant women residing within 0-3km of 1+ site pre-drilling (unexposed) vs. post-drilling (exposed), and then compares those women to a contemporaneous temporal control group residing 3-10km away in a pre-drilling vs. post-drilling context. We use logistic regression models and control for sociodemographic, behavioral, and clinical information.

Results: Among pregnant women residing 0-1km of an active drilling site, we find a 7% increased odds of gestational hypertension (95% CI: 1.02, 1.12) and a 28% increased odds of eclampsia (95% CI: 1.03, 1.58). These associations dissipate for residences 1-2 and 2-3km of 1+ drilling site during pregnancy. In restricted models, we find persistent associations among nulliparous women for gestational hypertension (1.15; 95% CI: 1.07, 1.23) and eclampsia (1.64; 95% CI: 1.23, 2.19).

Conclusions: Residential location less than 1km from an oil or gas extraction site, which aligns with hypothesized air pollution gradients from drilling sites, is associated with increased odds of gestational hypertension and eclampsia.