Pregnant women who take a common diabetes drug face a higher risk of having overweight children, research suggests.
The study, which contradicts previous trials, found youngsters had a BMI of 0.7 points higher if their mother used metformin.
Norwegian scientists concluded the drug – which lowers blood sugar – can cross the placenta and reach the growing foetus.
Children whose mothers used metformin during pregnancy also tended to weigh more when they turned four, by around 1lb 12oz (0.8kg).
Dr Liv Guro Engen Hanem, who led the study, described the results as ‘surprising’ because of an array of trials that showed the opposite.
‘Past research in this area had suggested metformin would have a protective effect on the children’s metabolic health,’ she said.
The study, branded ‘surprising’, found youngsters had a BMI of 0.7 points higher if their mother used metformin
It is the world’s most commonly prescribed diabetes drug and is given to millions of patients with type 2 – widely dubbed a silent killer.
But metformin is also dished out to polycystic ovary syndrome sufferers – a condition that strikes 10 per cent of women of reproductive age.
In this study, the mothers of around 160 children used in the study had all taken the drug to control their PCOS – a common cause of infertility.
It is not licenced for treating the condition, which raises the chances of developing diabetes, in the UK or US. But it is known to boost ovulation.
Some 161 children were measured by researchers at the Norwegian University of Science and Technology in Trondheim.
Their body weight and BMI were recorded when they turned six months old and on their fourth birthday. Head circumference and height were also tracked.
However, no differences were found for the latter features, according to the study published in The Journal of Clinical Endocrinology & Metabolism.
Children in the group of mothers who had taken metformin weighed, on average, 2st 12lbs (18.3kg) at four years old. Their counterparts weighed, on average, 2st 10lbs (17.5kg).
In terms of BMI, children in the group of mothers who had taken metformin had an average of 16.6. In comparison, their counterparts BMI was 15.9 on average.
Dr Hanem added: ‘Few studies have examined the long-term health of children born to women with PCOS who took metformin.
‘Our findings indicate more research is needed to determine its effects on children who were exposed in the womb.’
The findings are in stark contrast to what scores of diabetes patients claim – that metformin actually aids weight loss.
Diabetes.co.uk, a support website for sufferers, recognises that the drug can lower the appetite of patients and help them shed the pounds.
Metformin, sold as Glucophage in the UK and US, stops blood sugar levels from rising too high by blocking its release in the liver.
In turn, this means the body doesn’t have to produce as much insulin – which ‘acts on the brain to cause hunger’, Diabetes.co.uk states.