Background: β-Blockers are a class of antihypertensive medications that are commonly used in pregnancy.

Objective: To estimate the risks for major congenital malformations associated with first-trimester exposure to β-blockers.

Design: Cohort study.

Setting: Health registries in the 5 Nordic countries and the U.S. Medicaid database.

Patients: Pregnant women with a diagnosis of hypertension and their offspring.

Measurements: First-trimester exposure to β-blockers was assessed. Outcomes were any major congenital malformation, cardiac malformations, cleft lip or palate, and central nervous system (CNS) malformations. Propensity score stratification was used to control for potential confounders.

Results: Of 3577 women with hypertensive pregnancies in the Nordic cohort and 14 900 in the U.S. cohort, 682 (19.1%) and 1668 (11.2%), respectively, were exposed to β-blockers in the first trimester. The pooled adjusted relative risk (RR) and risk difference per 1000 persons exposed (RD1000) associated with β-blockers were 1.07 (95% CI, 0.89 to 1.30) and 3.0 (CI, −6.6 to 12.6), respectively, for any major malformation; 1.12 (CI, 0.83 to 1.51) and 2.1 (CI, −4.3 to 8.4) for any cardiac malformation; and 1.97 (CI, 0.74 to 5.25) and 1.0 (CI, −0.9 to 3.0) for cleft lip or palate. For CNS malformations, the adjusted RR was 1.37 (CI, 0.58 to 3.25) and the RD1000 was 1.0 (CI, −2.0 to 4.0) (based on U.S. cohort data only).

Limitation: Analysis was restricted to live births, exposure was based on dispensed medication, and cleft lip or palate and CNS malformations had few outcomes.

Conclusion: The results suggest that maternal use of β-blockers in the first trimester is not associated with a large increase in the risk for overall malformations or cardiac malformations, independent of measured confounders.