Summary: Metformin is an effective drug that has been used in the treatment of type 2 diabetes, pre-diabetes and as an adjuvant in the treatment of PCOS for many years. Its action consists primarily in inhibiting hepatic gluconeogenesis and increasing glucose uptake by peripheral tissues, mainly muscles. Numerous studies have shown that the use of metformin in GDM (Gestational Diabetes Mellitus) is not only as effective as insulin treatment, but also prevents excessive weight gain among pregnant women while not exposing them to the risk of hypoglycemia. The oral form of administration significantly increases therapeutic compliance. Metformin used in the first months of pregnancy among women treated for PCOS reduces the risk of miscarriage. So far, the benefit of metformin in pregnancy among obese women without concomitant diabetes has not been demonstrated. Long-term follow-up care of the children of women treated with metformin during pregnancy showed no significant abnormalities.