Metformin in women with type 2 diabetes in pregnancy (MiTy): a multicentre, international, randomised, placebo-controlled trial

RCT (n=502) found that women achieved better glycaemic control, lower doses of insulin and reduced weight gain when metformin was added to insulin vs placebo. Metformin exposed infants were more likely to be small for gestational age however (13% vs 7%, RR 1.96, p=0.026).

SPS commentary:

Authors conclude that understanding the implications of these effects on infants will be important to properly advise patients who are contemplating the use of metformin during pregnancy.

A related commentary provides some background, stating that some centres have been using metformin during pregnancy since the late 1970s, and evidence from mostly observational or unmasked randomised studies has suggested that the combination of metformin with insulin during the second and third trimesters can improve maternal glycaemic control without adverse effects to the mother, foetus, or neonate.

It highlights that in women with diabetes, the second and third trimesters are associated with escalating insulin resistance, and metformin acts to counter the clinical effects of insulin resistance (without weight gain or hypoglycaemia). Thus, metformin could better assist metabolic control during the later stages of pregnancy. This study found no apparent differences in the neonatal outcomes of pregnancies in which metformin was started before versus after 16 weeks’ gestation, or use of metformin in women with obesity versus women without obesity. It concludes that this study has provided prospective, controlled evidence to support the low-cost, potentially beneficial, metabolic effects of metformin with insulin in the management of pregnancy for type 2 diabetes and gestational diabetes, and substantiated a generally favourable safety profile for neonates.


The Lancet Diabetes & Endocrinology

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