Asthma affects 5% to 13% of pregnant women, and many require daily pharmacotherapy to achieve asthma control; however, adherence to medication during pregnancy often decreases.

Using linked population-based administrative databases from Alberta, Canada (2012-2018), pregnant women with asthma were categorized based on asthma medication use 1 year before pregnancy: short-acting β-agonists (SABA), inhaled corticosteroids (ICS), and ICS with long-acting β-agonists (ICS+LABA). Women on ICS+LABA were grouped by trajectory of adherence during pregnancy using group-based trajectory modeling. Logistic regressions were used to estimate the associations between the use of or trajectories of adherence to asthma medication during pregnancy with asthma exacerbation and maternal/neonatal outcomes.

Overall, 13,509 of 238,751 (5.7%) pregnant women had asthma before pregnancy (SABA: 24.7%; ICS: 12.5%; ICS+LABA: 25.1%; none: 36.1%). The use of SABA (adjusted odds ratio [aOR]: 1.79, 95% confidence interval [CI]: 1.21, 2.64), ICS (aOR: 3.37, 95% CI: 2.10, 5.39), and ICS+LABA (aOR: 3.64, 95% CI: 2.57, 5.17) had greater odds of disease exacerbation than no asthma medication during pregnancy. ICS+LABA adherence groups during pregnancy included low (79.8%), moderate-to-decreasing (14.0%), and moderate-to-increasing (6.2%). The moderate-to-decreasing (aOR: 1.45, 95% CI: 1.14, 1.84) and moderate-to-increasing (aOR: 2.06, 95% CI: 1.50, 2.83) adherence groups had greater odds of disease exacerbation than the low adherence group. ICS use during pregnancy decreased odds of preterm birth (aOR: 0.62; 95% CI: 0.39, 0.99) and neonatal intensive care unit admission (aOR: 0.66; 95% CI: 0.45, 0.97). Other group comparisons were not statistically significant.