Metoprolol

Pregnancy

Birth defects: MotherToBaby says the metoprolol-specific risk is not known. Bateman et al. (2018) studied first-trimester beta-blocker exposure in 3,577 hypertensive pregnancies in Nordic registries and 14,900 in the U.S. Medicaid database. The pooled adjusted relative risk was 1.07 (95% CI 0.89 to 1.30) for any major malformation and 1.12 (0.83 to 1.51) for heart defects. This was beta-blocker class-level evidence, not a metoprolol-only estimate, and the study included live births only. Miscarriage: MotherToBaby says studies have not been done to test whether metoprolol can increase miscarriage chance. The abstract of a 2017 prospective cohort reports no evidence of increased early pregnancy loss in a sensitivity comparison of methyldopa monotherapy with metoprolol monotherapy. The study focused on methyldopa, and its abstract does not give a standalone metoprolol risk estimate. DailyMed labeling says published observational studies have not demonstrated an association with miscarriage. Bateman et al. (2018) studied only live births and cannot answer miscarriage risk. Fetal growth: Tanaka et al. (2016) reviewed 158 pregnancies in people with cardiovascular disease; the beta-blocker group included 12 metoprolol pregnancies, with fetal growth restriction reported in 17%. This was a small, retrospective, single-center cohort. Duan et al. (2018) studied 379,238 singleton pregnancies, including 324 metoprolol-exposed pregnancies; metoprolol's adjusted odds ratio for small-for-gestational-age birth was 1.5 (95% CI 0.9 to 2.3), which was not statistically significant. Kayser et al. (2020) compared 294 neonates exposed to metoprolol or bisoprolol with methyldopa-exposed and nonhypertensive groups; long-term beta-blocker exposure was associated with more small-for-gestational-age births, but the two beta-blockers were combined and maternal hypertension could contribute. ROPAC (Ramlakhan et al., 2024) included 5,739 pregnancies with heart disease; 875 had beta-blocker exposure, including 323 metoprolol exposures. The exposed beta-blocker group had more small-for-gestational-age infants, but the overall result was class-level and cannot be attributed to metoprolol alone. ACOG's CHAP advisory describes a randomized treatment-strategy trial of 2,408 pregnancies with chronic hypertension: small-for-gestational-age birth was 11.2% in the treatment group and 10.4% in the control group. CHAP did not test metoprolol specifically; its protocol used standard antihypertensive strategies, chiefly labetalol or extended-release nifedipine. A 2026 single-center study of 57 beta-blocker-exposed pregnancies and 165 controls found lower average birth weight and more growth restriction, but exposure was mainly nadolol and bisoprolol and the study did not estimate a metoprolol-specific effect. A 2026 case report described one newborn with hypoglycemia after prenatal metoprolol; a single case cannot estimate frequency. Current U.S. metoprolol labels state that growth, preterm-birth, and perinatal-mortality findings are inconsistent and methodologically limited. Neurodevelopment: Peeples et al. (2026) analyzed 6,135,213 linked children in U.S. Epic Cosmos records born from 2014 to 2023, with at least 18 months of follow-up. Figure 3 lists 1,750 autism diagnoses among 34,492 children with maternal metoprolol prescription exposure (5.1%) and an adjusted hazard ratio of 1.35 (95% CI 1.29 to 1.41) compared with no SBIM exposure. The supplementary sensitivity model accounting for psychiatric diagnoses still estimated an adjusted hazard ratio of 1.27 (95% CI 1.21 to 1.33). The study counted prescriptions, dispensations, administrations, or orders overlapping pregnancy, did not report trimester-specific or dose-duration effects, and acknowledged no independent confirmation of autism diagnoses and incomplete control of possible comorbidities. This is one observational association and does not establish that metoprolol caused the difference; no independent replication was found in the reviewed literature.

Breastfeeding

Ryu et al. (2016) measured metoprolol levels in milk and found relative infant exposure below 1% of the mother's weight-adjusted dose in three lactating women. LactMed (last revised 15 November 2024) summarizes additional small studies and case reports, including a mean relative infant dose of 0.5% in three mothers, undetectable metoprolol in some infant blood samples, and no reported adverse effects in the small reports it reviews. LactMed advises monitoring for slow heart rate and listlessness related to low blood sugar. Current DailyMed labeling estimates a relative infant dose of 0.5% to 2%, reports no identified adverse reactions in breastfed infants, and recommends monitoring for signs of beta-blockade. NHS SPS lists metoprolol among preferred beta-blockers during breastfeeding for full-term, healthy infants and recommends monitoring for slow heart rate, low blood sugar, sleepiness, poor feeding, and inadequate weight gain. Freppel et al. (2024) interviewed 53 women treated with beta-blockers; 27 breastfed and no serious adverse event was observed, but the study did not provide a metoprolol-specific infant outcome estimate. Evidence for premature or medically ill infants is limited.

What was tested

Pregnancy evidence includes observational population cohorts, small cardiovascular-disease cohorts, a global registry of pregnancies with heart disease, and a large late-pregnancy newborn-outcome cohort. CHAP was a randomized trial of a chronic-hypertension treatment strategy, not a metoprolol trial. The largest first-trimester malformation study examined beta-blockers as a class and was limited to live births. A 2026 U.S. electronic-record cohort reported a metoprolol-specific association with later autism diagnoses, but did not distinguish trimester or establish causation. Breastfeeding evidence includes small milk-level and infant-level studies, case reports, and a 2024 prospective cohort of beta-blocker users. No randomized metoprolol-specific pregnancy or breastfeeding outcome trial is cited in the sources used here.