Women with Type 2 diabetes who take the blood glucose lowering drug metformin during pregnancy are more likely to see various health benefits, including requiring less insulin, less weight gain and a reduction in their risk of a caesarean birth, according to a new study from Sinai Health.

The study, whose findings are out today in Lancet Diabetes & Endocrinology, examined 502 pregnant women with Type 2 diabetes from 29 centres in Canada and Australia. The women were randomized to receive either metformin, a common drug used to treat Type 2 diabetes, or placebo, in addition to their usual insulin regimen.

“Women with Type 2 diabetes are often on metformin prior to pregnancy,” said study author Dr. Denice Feig. “Once pregnant, there is little evidence to guide their decision to either stop the metformin, or continue throughout pregnancy. This research aims to help further guide their decision.”

The MiTy-trial is the first large, multi-centre, international, double-masked, placebo-controlled trial of its kind in pregnant women with Type 2 diabetes. The team worked with a number of researchers across Canada and Australia, including Dr. Kellie Murphy from Mount Sinai Hospital and Dr. David Simmons from Australia.

Feig, a clinician scientist at the Lunenfeld-Tanenbaum Research Institute and head of the Diabetes and Endocrinology in Pregnancy program at Mount Sinai Hospital, said metformin-treated women and their infants had several benefits, including better glucose control, lower insulin requirements, less gestational weight gain, and fewer caesarean births than women in the placebo group.

Diabetes in the mother is one of the most common causes of large babies. This study showed that infants of mothers taking metformin weighed 210 grams less, and were less likely to be extremely large for gestational age.

However, Feig warned infants should be monitored closely while in utero to see if they are gaining enough weight.

“We found several maternal benefits and infant benefits in the metformin group, with fewer large infants, but more small infants,” Feig said. “Women can be told of these many benefits, but caregivers may need to pay attention to those infants who may be growing too slowly and in that situation the drug should be stopped.”

Type 2 diabetes is the most common type of diabetes affecting nearly 500 million people worldwide.

Feig said next steps are to look at the long-term effects of metformin on infants in order to provide the best possible advice to expecting mothers.