A study of almost 1.5 million children has found the risk of epilepsy almost doubled among those born to severely obese mums.

Being overweight during the first trimester of pregnancy has been linked to an increased risk of childhood epilepsy.

A Swedish study of almost 1.5 million babies found the risk of epilepsy almost doubled from normal-weight women to very severely obese women.

Epilepsy disrupts the normal electrochemical activity of the brain resulting seizures.

The cause of this debilitating and often hard-to-treat condition is poorly understood.

With obesity on the rise, there is growing concern about the long-term neurological effects of children exposed to maternal obesity in pregnancy.

"Given that overweight and obesity are potentially modifiable risk factors, prevention of obesity in women of reproductive age may be an important public health strategy to reduce the incidence of epilepsy," the authors wrote.

Researchers at the Karolinska Institutet in Stockholm studied the nearly 1.5 million live-births in Sweden between 1997 and 2011. Of those, there were 7592 babies, 0.5 per cent, diagnosed with epilepsy.

The risk of epilepsy increased by 11 per cent among those born to overweight mothers - with a body mass index of 25-29 - compared with children of normal-weight mothers.

Grade I obesity (BMI 30 to less than 35) was associated with a 20 per cent increased risk, grade II obesity (BMI 35 to less than 40) was associated with a 30 per cent increased risk.

Babies born to severely obese mums, or grade III obesity, was associated with an 82 per cent increased risk of epilepsy.

The study has been published in journal BMJ Neurology.

One possible reason for this increased risk, according to the authors, is that being overweight and obesity may increase the risk of brain injury, leading to a range of neurodevelopmental disorders.

Another possible reason is that maternal obesity might affect neuro-development through obesity-induced inflammation.

However the authors note the study had limitations including possible misclassification and under-reporting, and that the cause of epilepsy may be both genetic and environmental.