Pregnancy & breastfeeding
Metformin (Glucophage) in pregnancy and breastfeeding
Biguanide (glucose-lowering) · Type 2 diabetes; used in gestational diabetes and polycystic ovary syndrome
Pregnancy
Acceptable; insulin often preferredMetformin does not appear to cause birth defects, and in trials for gestational and type 2 diabetes it gave similar newborn outcomes to insulin or placebo, with less maternal weight gain. It crosses the placenta, and some exposed children have been heavier in follow-up studies, which is one reason U.S. obstetric guidance has preferred insulin when medication is needed.[1, 2, 3, 4]
Breastfeeding
Compatible with breastfeedingMilk levels are low: infants receive under 0.5% of the mother's weight-adjusted dose, and a sizeable prospective study found no adverse effects. Use with more caution for newborns, premature infants and infants with kidney problems.
Written for clinicians. If you are pregnant or breastfeeding, talk to your clinician before you start, stop or change any medicine.
Ask EvidencePulse about metformin
Get a cited answer from the newest studies, for your patient's trimester or your question.
What the human data show
Metformin is randomized-trial tested in pregnancy, which is unusual. The trials answer the short-term questions well; offspring follow-up is still accumulating.
Randomized trial vs insulin (MiG) · Australia and New Zealand · 2008
751 women with gestational diabetes at 20-33 weeks.
No difference in the composite of neonatal complications; women preferred metformin. Nearly half needed supplemental insulin.[2]
Composite outcome 32.0% vs 32.2% (RR 0.99, 0.80-1.23). Supplemental insulin 46.3%.
Randomized placebo-controlled trial (MiTy) · Canada and Australia · 2020
502 women with type 2 diabetes on insulin.
No difference in the neonatal composite; better glucose control, less weight gain and fewer cesareans, smaller babies, and more small-for-gestational-age infants.[3]
Composite 40% vs 40% (RR 1.02). Weight gain 7.2 vs 9.0 kg. Cesarean 53% vs 63%. SGA 13% vs 7% (RR 1.96, 1.10-3.64).
Trial follow-up of children (MiTy Kids) · Canada and Australia · 2023
283 children at 24 months.
No difference in BMI z-score or skinfolds overall.[5]
BMI z 0.84 vs 0.91 (difference 0.07, -0.31 to 0.45).
Trial follow-up of children (PedMet, after PregMet) · Norway · 2019
141 children aged 5-10 whose mothers with PCOS took metformin or placebo in pregnancy.
Higher BMI z-scores in metformin-exposed children.[6]
Difference in BMI z 0.41 (0.03-0.78).
Case-control with malformed controls (EUROmediCAT) · Europe · 2018
50,167 babies with congenital anomalies; 168 exposed to metformin.
No increase in non-genetic anomalies overall; one signal (pulmonary valve atresia) consistent with chance.[1]
All non-genetic anomalies aOR 0.84 (0.55-1.30).
Poorly controlled diabetes itself raises the risk of birth defects (6 to 10% when HbA1c is over 7%, per the label), stillbirth and macrosomia, so the comparison that matters is metformin versus other ways of controlling glucose.
The FDA label, summarized
Current metformin labels say published studies have not shown a clear association with major birth defects, miscarriage or adverse maternal or fetal outcomes, while noting the limits of those studies, and that animal studies showed no developmental harm at 2 to 5 times a 2,550 mg dose.
They emphasize the risks of poorly controlled diabetes in pregnancy (ketoacidosis, preeclampsia, miscarriage, preterm birth, stillbirth, macrosomia) and give a background malformation risk of 6 to 10% with HbA1c above 7%, up to 20 to 25% above 10%.
- Label
- METFORMIN HYDROCHLORIDE (Quallent Pharmaceuticals Health LLC), effective Aug 12, 2026 · Full label on DailyMed
- Former FDA letter category
- B (the FDA retired letter categories in 2015; labels now describe the data instead)
LactMed: infant exposure and effects
LactMed: milk levels are low and steady, so timing feeds around doses does not help. Infants receive under 0.5% of the weight-adjusted maternal dose, though metformin is sometimes detectable at low levels in their serum. One sizeable prospective study found no adverse effects.
Effects in breastfed infants
Healthy growth and development were reported in small follow-up series. Use with caution in newborns, premature infants and infants with renal impairment.
Effects on milk supply
Sometimes tried as a galactagogue; there is no evidence that it increases supply.
- Source
- LactMed® record “Metformin”, revised Aug 15, 2026 · Open the record
Alternatives to consider
- Insulin
Does not cross the placenta; the preferred medication for gestational diabetes in ACOG's 2018 guidance.[4]
- Glyburide
Crosses the placenta; generally considered inferior to insulin and metformin in recent trials and guidance.
2MM+
New pregnancy and lactation studies, the day they publish
2MM+ members read every 2 Minute Medicine summary in full, with unlimited EvidencePulse questions and the NPI Lookup member tools.
Questions clinicians ask
Is metformin safe in early pregnancy?
First-trimester metformin has not been linked to birth defects; a European analysis found no increase in congenital anomalies overall (aOR 0.84). Women with PCOS who conceive on metformin should discuss whether to continue.[1]
Metformin or insulin for gestational diabetes?
Both control glucose with similar newborn outcomes in trials. Metformin is easier and preferred by many patients, but about half need insulin added, and long-term child effects are less certain, so U.S. obstetric guidance has favored insulin.[2, 4]
Does metformin in pregnancy affect the child's weight?
Results differ by population: no difference at 2 years in children of mothers with type 2 diabetes (MiTy Kids), but higher BMI z-scores at 5-10 years after PCOS treatment (PedMet).[5, 6]
Can I take metformin while breastfeeding?
Yes. Infants receive less than 0.5% of the maternal dose; extra caution applies to newborns, premature infants and infants with kidney problems.
References
- Given JE, Loane M, Garne E, et al. Metformin exposure in first trimester of pregnancy and risk of all or specific congenital anomalies: exploratory case-control study. BMJ. 2018;361:k2477. PubMed · DOI
- Rowan JA, Hague WM, Gao W, et al. Metformin versus insulin for the treatment of gestational diabetes. N Engl J Med. 2008;358(19):2003-2015. PubMed · DOI
- Feig DS, Donovan LE, Zinman B, et al. Metformin in women with type 2 diabetes in pregnancy (MiTy): a multicentre, international, randomised, placebo-controlled trial. Lancet Diabetes Endocrinol. 2020;8(10):834-844. PubMed · DOI
- ACOG Practice Bulletin No. 190: Gestational diabetes mellitus. Obstet Gynecol. 2018;131(2):e49-e64. PubMed
- Feig DS, Sanchez JJ, Murphy KE, et al. Outcomes in children of women with type 2 diabetes exposed to metformin versus placebo during pregnancy (MiTy Kids): a 24-month follow-up of the MiTy randomised controlled trial. Lancet Diabetes Endocrinol. 2023;11(3):191-202. PubMed · DOI
- Hanem LGE, Salvesen Ø, Juliusson PB, et al. Intrauterine metformin exposure and offspring cardiometabolic risk factors (PedMet study): a 5-10 year follow-up of the PregMet randomised controlled trial. Lancet Child Adolesc Health. 2019;3(3):166-174. PubMed · DOI
The free Daily Brief
Doctor-written summaries of the day's most important studies, in your inbox every morning.
Your subscription opens securely in a new tab. No spam.
Get the app