Metformin is an antihyperglycaemic biguanide used in the management of type 2 diabetes. It acts by lowering basal and postprandial plasma glucose without stimulating insulin secretion, thereby reducing the risk of hypoglycaemia associated with insulin therapy. Metformin is also used off-label for the treatment of infertility secondary to polycystic ovarian syndrome (PCOS).
The available data do not show an increased risk of congenital malformation, spontaneous abortion, preterm delivery, small or large for gestational age infants, perinatal mortality or neonatal complications. However, there are insufficient data relating to metformin exposure in early pregnancy to exclude an increased risk of congenital malformations or spontaneous abortion. NICE guidance states that women with diabetes may be advised to use metformin as an adjunct or alternative to insulin in the preconception period and during pregnancy, when the likely benefits from improved blood glucose control outweigh the potential for harm.
Exposure to metformin at any stage of pregnancy would not usually be regarded as medical grounds for termination of pregnancy or any additional fetal monitoring over and above that recommended for women with diabetes in pregnancy. However, other risk factors may be present in individual cases which independently increase the risk of adverse pregnancy outcome. Clinicians are reminded of the importance of consideration of such factors when performing case-specific risk assessments.
This is a summary of the full UKTIS monograph for health care professionals and should not be used in isolation. The full UKTIS monograph and access to any hyperlinked related documents is available to NHS health care professionals who are logged in.
If you have a patient with exposure to a drug or chemical and require assistance in making a patient-specific risk assessment, please telephone UKTIS on 0344 892 0909 to discuss the case with a teratology specialist.
If you would like to report a pregnancy to UKTIS please click here to download our pregnancy reporting form. Please encourage all women to complete an online reporting form.