Pregnancy: Determination of fetal concentrations of metformin hydrochloride suggest that a partial placental barrier to the drug exists. Since abnormal maternal blood glucose concentrations during pregnancy may be associated with a higher incidence of congenital abnormalities, most experts recommend that insulin be used during pregnancy to maintain optimum control of blood glucose concentration.
Lactation: Metformin hydrochloride is distributed into breastmilk. A decision should be made whether to discontinue nursing or the drug, taking into account the importance of the drug to the woman. If metformin hydrochloride is discontinued in a nursing mother and dietary therapy is inadequate for glycemic control, insulin therapy should be considered.