Treating obese pregnant women with a diabetes drug does not stop their babies from being born overweight, a study has found.

Heavier babies are more likely to grow into overweight adults and doctors had hoped the treatment would help to reduce obesity rates as well as lower the number of difficult births.

The research, which was led by the University of Edinburgh, tested whether treating overweight mothers-to-be with the diabetes drug metformin, which helps to regulate blood sugar, would reduce the weight of their babies.

They treated 226 obese pregnant women with the medication from their second trimester until their babies were born.

There was no difference in the weight of babies born to mothers who received the treatment compared with a group of 223 women who received a dummy pill

But they found there was no difference in the weight of babies born to mothers who received the treatment compared with a group of 223 women who received a dummy pill.

Metformin also had no effect on the number of birth complications, such as miscarriages and still births.

The treatment did help to reduce blood sugar levels in the mothers-to-be and helped to lower the levels of other markers linked to pre-eclampsia and pre-mature births.

Researchers said they would need to follow the babies involved in the study for longer to determine whether the treatment lowered their chances of developing other health problems in later life.