Discontinue Metformin Once Pregnancy is Confirmed
No, metformin should be discontinued immediately once pregnancy is confirmed in women with PCOS, as there is no evidence-based need to continue it during pregnancy, and long-term offspring data show concerning metabolic trends including higher BMI and increased obesity rates in children exposed to metformin in utero. 1
Guideline-Based Recommendation
The American College of Obstetricians and Gynecologists explicitly states there is no evidence-based need to continue metformin in PCOS patients once pregnancy has been confirmed. 2, 1 Randomized, double-blind, controlled trials comparing metformin with other therapies for ovulation induction in women with PCOS have demonstrated no benefit in preventing spontaneous abortion or gestational diabetes once pregnancy occurs. 2, 1
Why Metformin Was Useful Before Pregnancy—But Not During
- Metformin's role in PCOS is to improve insulin sensitivity, reduce androgen levels, and restore ovulation in women attempting to conceive. 2, 3
- Once pregnancy is achieved, these preconception benefits no longer apply, and the risk-benefit ratio shifts unfavorably. 1
- The metabolic improvements that helped achieve pregnancy do not translate into pregnancy benefits that outweigh potential offspring risks. 2, 1
Placental Transfer and Offspring Concerns
- Metformin readily crosses the placenta, with umbilical cord blood levels equal to or higher than maternal levels. 2, 1
- Long-term follow-up studies of children exposed to metformin in utero show concerning trends:
- 9-year-old offspring had higher BMI, increased waist-to-height ratio, and greater waist circumference in the Auckland cohort of the MiG TOFU study. 2
- 4-year-old offspring from PCOS pregnancies showed higher BMI and increased obesity. 2
- 5-10 year follow-up demonstrated higher BMI, weight-to-height ratios, waist circumferences, and borderline increase in fat mass. 2
- A recent meta-analysis concluded that metformin exposure resulted in smaller neonates with acceleration of postnatal growth resulting in higher BMI in childhood. 2
Common Pitfall to Avoid
Do not continue metformin "just in case" based on its preconception benefits—the evidence shows no benefit for preventing miscarriage or gestational diabetes once pregnancy is confirmed, while offspring metabolic concerns persist. 2, 1
Specific Contraindications During Pregnancy
Metformin should absolutely not be used in pregnant women with:
- Hypertension or preeclampsia 2, 1
- Risk for intrauterine growth restriction 2, 1
- Placental insufficiency concerns (due to potential for growth restriction or acidosis) 2
What to Do Instead
- Discontinue metformin immediately upon positive pregnancy test. 1
- Transition to pregnancy-appropriate management for glucose control if needed—insulin is the preferred agent for diabetes management in pregnancy. 2, 1
- For women with GDM requiring medical therapy who cannot safely use insulin due to cost, language barriers, or cultural influences, oral agents may be considered only after discussion of known risks and need for long-term safety data, but this does not apply to PCOS patients who conceived on metformin. 2
Nuance: Conflicting Older Research Data
While some older observational studies suggested metformin continuation might reduce early pregnancy loss in PCOS women (11.6% vs 36.3% miscarriage rates) 4, and another study showed reduced pregnancy-induced hypertension and gestational diabetes with continuous use 5, these findings have not been confirmed in higher-quality randomized controlled trials. 2, 1 The most recent and authoritative guideline evidence from ACOG (2021) and systematic reviews (2025) supersede these earlier observational findings and emphasize the lack of evidence-based need for continuation plus concerning long-term offspring data. 2, 1, 3