Asthma has been linked with an increased risk of pregnancy induced hypertension (PIHT), but it is unclear whether this association is due to medication or the condition itself. This nested case-control study selected a cohort of asthmatic pregnant women from 1990 to 2000 and identified 302 cases of PIHT from a total of 4593 pregnancies. Cases of PIHT were compared with suitably matched controls. In both groups the use and dosage of inhaled corticosteroids were analysed using two conditional logistic regression models. Use of inhaled corticosteroids during pregnancy was not associated with any increased risk of PIHT (adjusted OR 1.02, 95% CI 0.77 to 1.34) or pre-eclampsia. In contrast, both oral corticosteroids and markers of uncontrolled/severe asthma were associated with a statistically significant increased risk of PIHT (oral corticosteroids: adjusted OR 1.57, 1.02 to 2.41). Markers of uncontrolled asthma included visits to the emergency department for asthma, use of oral corticosteroids, and having been reviewed by a respiratory specialist.

Asthma during pregnancy can result in potentially serious complications including PIHT. This study suggests that the use of inhaled corticosteroids for the control of asthma in pregnancy does not increase the risk of PIHT or pre-eclampsia.