Beta‐blocker subtypes and risk of low birth weight in newborns

Beta-blockers are one of the most commonly prescribed classes of antihypertensive medications during pregnancy. Previous studies reported an association between beta-blocker exposure and intrauterine growth restriction. Whether some beta-blocker subtypes may be associated with higher risk is not known. This is a retrospective cohort study of pregnant women exposed to beta-blockers in the Kaiser Permanente Southern California Region between 2003 and 2014. Logistic regression models were used to evaluate association between exposure to different beta-blocker agents and risk of low fetal birth weights. In a cohort of 379 238 singleton pregnancies, 4847 (1.3%) were exposed to beta-blockers. The four most commonly prescribed beta-blockers were labetalol (n = 3357), atenolol (n = 638), propranolol (n = 489), and metoprolol (n = 324). Mean birth weight and % low birth weight (<2500 g) were 2926 ± 841 g and 24.4% for labetalol, 3058 ± 748 g and 18.0% for atenolol, 3163 ± 702 g and 13.3% for metoprolol, 3286 ± 651 g and 7.6% for propranolol, and 3353 ± 554 g and 5.2% for non-exposed controls. Exposure to atenolol and labetalol were associated with increased risks of infant born small for gestational age (SGA) (atenolol: adjusted OR 2.4, 95% CI: 1.7-3.3; labetalol: adjusted OR 2.9, 95% CI: 2.6-3.2). Risk of SGA associated with metoprolol or propranolol exposure was not significantly different from the non-exposed group (metoprolol: adjusted OR 1.5, 95% CI: 0.9-2.3; propranolol: adjusted OR 1.3, 95% CI: 0.9-1.9). Association between beta-blocker exposure and SGA does not appear to be a class effect. Variations in pharmacodynamics and confounding by indication may explain these findings.