Metoprolol during pregnancy: heart rate and blood pressure safety

What does the evidence say about metoprolol during pregnancy?

1. MotherToBaby reports no studies answering miscarriage risk and insufficient metoprolol-specific data to determine birth-difference risk; a large beta-blocker study did not show an increased rate of fetal heart differences. 1
2. A prospective cohort of hypertensive pregnancies found small-for-gestational-age birth in 24.1% after long-term metoprolol or bisoprolol exposure versus 10.2% with methyldopa and 9.9% in nonhypertensive pregnancies, with significant adjusted associations. 2
3. In a Medicaid cohort of more than 2.29 million live births, beta-blocker exposure at delivery was associated with neonatal hypoglycemia and bradycardia after adjustment; this was a class analysis and not a metoprolol-only estimate. 3
4. A contemporary arrhythmia review says many pregnancy palpitations and arrhythmias are benign, but persistent or higher-risk rhythms require clinical identification and multidisciplinary management before deciding whether an antiarrhythmic such as a beta blocker is appropriate. 4
5. LactMed reports low metoprolol levels in milk, an average relative infant dose of 0.5% in one small series, and no reported adverse effects in the limited breastfeeding studies, while advising monitoring for beta-blockade symptoms. 5

Is metoprolol safe in each trimester?

• First trimester. Metoprolol-specific miscarriage and major-malformation evidence remains limited. MotherToBaby notes that a large beta-blocker study did not find more fetal heart differences, but class findings cannot answer every metoprolol dose or indication.
• Second trimester. Long-term metoprolol or bisoprolol exposure in hypertensive pregnancies was associated with more small-for-gestational-age births than both methyldopa and nonhypertensive comparison groups. Maternal hypertension still confounds how much of the difference is medication-related.
• Third trimester. Make sure the delivery and newborn teams know about current metoprolol use. A large beta-blocker class cohort found higher adjusted odds of newborn hypoglycemia and bradycardia after exposure at delivery, supporting planned neonatal observation.