NEW ORLEANS – The use of labetalol or atenolol in pregnancy is associated with significantly increased risk of having a small-for-gestational-age (SGA) baby; metoprolol and propranolol are not.
And none of these four beta-blockers are associated with increased risk of congenital cardiac anomalies, Angie Ng, MD, reported at the American Heart Association scientific sessions.
Dr. Angie Ng
Overall, the average birth weight for babies whose mothers were on a beta-blocker was 2,996 g, significantly less than the 3,353 g in 374,391 controls who weren’t exposed to beta-blockers during pregnancy. But beta-blockers are not a monolithic class of drugs; their pharmacokinetics and physical properties differ. And so did their associated incidence of SGA, according to Dr. Ng of Kaiser Permanente Los Angeles.
The rate of SGA below the 10th percentile was 17.6% in the 3,357 women on labetalol during pregnancy and the same in the 638 women on atenolol. In contrast, the SGA rates in women on metoprolol or propranolol – 10.8% and 10.3%, respectively – weren’t significantly different from the 8.7% incidence in controls.
To deal with the possibility of confounding by indication, Dr. Ng and her coinvestigators performed a multivariate analysis adjusted for maternal age, white race, body mass index, gestational age, diabetes, hypertension, arrhythmias, dyslipidemia, and renal insufficiency. The resultant adjusted risk of having an SGA baby was 2.9-fold greater in women on labetalol and 2.4-fold greater in those on atenolol than in controls. Women on the other two beta-blockers faced no increased risk.
The incidence of congenital cardiac anomalies was 5.1% in women exposed to beta-blockers in pregnancy and 1.9% in controls who weren’t. The most commonly diagnosed anomalies – patent ductus arteriosus, atrial septal defect, and ventricular septal defect – were two- to threefold more frequent in the setting of maternal beta-blocker exposure. However, in a multivariate analysis the use of any beta-blocker was no longer associated with significantly elevated risk of congenital cardiac anomalies.
“This suggests that the initial association we see in the unadjusted analysis is likely due to confounders and not due to the beta-blocker exposure,” Dr. Ng said.
Labetalol and atenolol were prescribed during pregnancy most often for hypertension, while metoprolol and propranolol were typically prescribed to control arrhythmias.
Previous reports by other investigators have yielded conflicting results as to whether maternal beta-blocker therapy is associated with increased risk of SGA. A major limitation of those studies was that they examined beta-blockers as a class rather than assessing the impact of specific agents, according to Dr. Ng.
She reported having no financial conflicts of interest regarding her study, which was conducted free of commercial support.