Obese women in the U.K. will be given an anti-diabetes drug during pregnancy to stop their babies from being born overweight as part of a new study.

The trial—the first of its kind in the world—was launched following evidence of a sharp rise in the number of larger than average babies.

So-called large babies are those weighing more than 11 pounds. Large babies are twice as likely to become overweight adults.

Researchers at the University of Edinburgh will give 400 obese women the diabetes drug metformin during pregnancy. The drug should reduce the amount of energy reaching the baby in the womb.

"Metformin is a drug already taken by women during pregnancy if they have diabetes, so we know that it is safe," said Dr. Fiona Denison, of the Queen's Medical Research Institute in Edinburgh.  "It works by reducing the mother's blood glucose to more normal levels. We are hoping that will lead to a healthier outcome for mother and baby."

Clinically obese pregnant women are more likely to develop diabetes and pre-eclampsia in pregnancy—and their babies are more prone to complications in the womb and to being stillborn.

"A good diet and exercise are paramount for any women in pregnancy," Denison said. "We are not saying that taking this pill removes the need for following that advice. It's an adjunct to that."

Nine hospitals around the U.K. are taking part in the trial. Results are not expected for at least two years.

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