Metformin Use in Pregnancy

Primary Recommendation

The American Diabetes Association recommends insulin as the gold standard and first-line pharmacologic treatment for gestational diabetes mellitus (GDM) and type 2 diabetes in pregnancy, due to metformin's potential to cross the placenta and concerns over long-term offspring safety 1, 2, 3
Insulin is preferred over metformin and glyburide as first-line agents because metformin and glyburide cross the placenta, raising concerns about long-term offspring safety 1, 4

Metformin may be considered as a second-line alternative for women who cannot use insulin safely or effectively due to cost barriers, language barriers, comprehension issues, or cultural factors, with thorough counseling about known risks and lack of complete long-term offspring safety data 1, 4
The American College of Obstetricians and Gynecologists advises against using metformin in pregnant women with hypertension, preeclampsia, or those at risk for intrauterine growth restriction due to potential for growth restriction or acidosis in the setting of placental insufficiency 1, 4

Treatment failure rates with metformin monotherapy are substantial, with 25-28% of women with GDM failing to achieve adequate glycemic control and requiring supplemental insulin, according to the American Diabetes Association 3, 5
Approximately one-quarter to one-third of cases may require addition of insulin when metformin is initiated, highlighting the need for close monitoring 3, 5

Metformin readily crosses the placenta, resulting in umbilical cord blood levels equal to or higher than maternal levels, which may impact offspring health, as noted by the Endocrine Society 1, 4
Meta-analyses demonstrate that metformin exposure results in smaller neonates with acceleration of postnatal growth leading to higher BMI in childhood, according to the Pediatric Endocrine Society 3, 1, 4

Metformin offers some short-term advantages, including lower risk of neonatal hypoglycemia compared to insulin, as reported by the American Academy of Pediatrics 1, 5, 4
Metformin use is associated with less maternal weight gain during pregnancy, which may be beneficial for women with gestational diabetes, according to the American College of Obstetricians and Gynecologists 1, 5, 4

For women with PCOS using metformin for ovulation induction, there is no evidence-based need to continue metformin once pregnancy is achieved, as stated by the American Society for Reproductive Medicine 2, 6
Randomized trials comparing metformin with other therapies for ovulation induction have not demonstrated benefit in preventing spontaneous abortion or GDM, highlighting the need for individualized treatment plans 2, 6

The American Diabetes Association recommends initiating lifestyle modifications and considering insulin as the first-line pharmacologic treatment for women with GDM, with metformin as a second-line alternative in specific circumstances 1, 2, 4
Close monitoring is necessary to anticipate treatment failure in approximately one-quarter of patients and to address potential long-term offspring concerns 3, 5