The women will take the diabetes drug metformin, which is used to help control blood sugar levels.
Experts from Edinburgh University hope the drug could reduce the risk of complications among obese mothers-to-be, who are more likely to suffer gestational diabetes, pre-eclampsia and to need a Caesarean section.
Obese mothers have also been found to be ten times more likely to suffer from chest infections compared with pregnant women of a healthy weight.
They are also more likely to suffer from headaches and heartburn and more than three times more likely to have carpal tunnel syndrome.
The university’s researchers will work alongside colleagues from Liverpool, Coventry and Sheffield.