Motherisk update: Metformin use during the first trimester of pregnancy: Is it safe?

Question: A pregnant patient with polycystic ovary syndrome asked me whether continuing metformin, which she was taking to treat infertility before her pregnancy, is safe for her fetus. She has heard that metformin is a "drug for diabetes." How safe is it to take metformin during the first trimester of pregnancy and beyond? Answer: Despite the traditional response that all oral hypoglycemic agents are absolutely contraindicated during pregnancy, evidence that metformin is probably safe during the first trimester of pregnancy and beyond is accumulating. Results of a recent meta-analysis by the Motherisk Program showed no increase in incidence of major malformations and a potential protective effect in this patient population.