Why was I advised to continue taking metformin (a medication for polycystic ovary syndrome (PCOS) and metabolic abnormalities) through the first trimester of pregnancy despite having mild PCOS and no diabetes?

Why Continue Metformin Through First Trimester in PCOS?

Your provider likely recommended continuing metformin through the first trimester based on older practice patterns or concerns about early pregnancy loss, but current evidence from the American Diabetes Association explicitly states there is no evidence-based need to continue metformin in women with PCOS once pregnancy is confirmed, unless you have type 2 diabetes requiring ongoing treatment. 1, 2

The Evidence Against Continuation

No Proven Pregnancy Benefits

• Randomized 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. 1, 2
• The American Diabetes Association guidelines from 2018,2021,2023, and 2024 consistently state there is no evidence-based need to continue metformin once pregnancy is achieved in PCOS patients without diabetes. 1, 2
• Metformin does not prevent gestational diabetes, even in high-risk women with obesity, PCOS, or insulin resistance. 1

Placental Transfer Concerns

• Metformin readily crosses the placenta, resulting in umbilical cord blood levels equal to or higher than maternal levels. 1, 2, 3
• This means your developing baby is exposed to the same or higher concentrations of metformin as you are throughout pregnancy. 1

Long-Term Offspring Metabolic Effects

The most concerning evidence comes from long-term follow-up studies of children exposed to metformin in utero:

• At 9 years old, children exposed to metformin for gestational diabetes treatment were heavier with higher waist-to-height ratios and waist circumferences compared to insulin-exposed children (MiG TOFU study, Auckland cohort). 1, 2
• Follow-up studies at 4-10 years showed offspring had higher BMI, weight-to-height ratios, waist circumferences, and borderline increases in fat mass. 1, 2
• Meta-analyses demonstrate metformin exposure results in smaller neonates with acceleration of postnatal growth, leading to higher BMI in childhood. 1, 2

Why Some Providers Still Recommend It

Historical Practice Patterns

• Some providers continue older practices based on theoretical concerns about early pregnancy loss, despite lack of supporting evidence. 4, 5
• One older observational study from 2008 suggested benefits, but this has not been confirmed in higher-quality randomized controlled trials. 6

Misunderstanding of Indications

• Metformin's role in helping you conceive (improving ovulation) does not translate to pregnancy benefits once conception occurs. 2, 7
• The preconception benefits are separate from pregnancy maintenance. 2, 7

Current Guideline Recommendations

When to Stop Metformin

• The American Diabetes Association recommends metformin should be discontinued by the end of the first trimester if it was used solely for PCOS and ovulation induction. 1, 2
• For women with mild PCOS and no diabetes (like your situation), discontinuation once pregnancy is confirmed is appropriate. 1, 2

Exceptions Where Continuation IS Appropriate

Metformin should only be continued during pregnancy if you have:

• Type 2 diabetes requiring ongoing treatment 1, 2
• Gestational diabetes that develops and cannot be controlled with lifestyle modifications alone (though insulin remains first-line) 1

Important Contraindications During Pregnancy

If you do continue metformin, it must be stopped immediately if you develop: 1, 2

• Hypertension or preeclampsia
• Risk factors for intrauterine growth restriction
• Suspected placental insufficiency
• Kidney disease

These conditions increase the risk of growth restriction or acidosis with metformin use. 1

What to Discuss With Your Provider

Key Questions to Ask

• "Do I have type 2 diabetes or just PCOS with insulin resistance?" (This determines if continuation is appropriate) 1
• "What specific pregnancy benefit are we hoping to achieve by continuing metformin?" (There should be a clear answer beyond "it helped you conceive") 1, 2
• "Are you aware of the long-term offspring metabolic concerns from recent studies?" (Share the MiG TOFU findings) 1

The Bottom Line

For mild PCOS without diabetes, the current highest-quality evidence supports discontinuing metformin once pregnancy is confirmed or by the end of the first trimester at the latest, as there is no demonstrated benefit for pregnancy outcomes and emerging concerns about long-term offspring metabolic health. 1, 2

Your provider may have been following older recommendations or may not be aware of the most recent guideline updates and long-term offspring data. The FDA label also notes that limited data exists and cannot definitively establish absence of risk. 3