Babies delivered by Caesarean section have a 20 percent higher risk than normal deliveries of developing the most common type of diabetes in childhood, according to a new study.

Researchers at Queen's University Belfast reviewed 20 studies that included about 10,000 children with type 1 diabetes and 1 million who did not have it.

The researchers said that differences in factors such as birth weight, mother's age and breast-feeding could not account for the higher diabetes rate.

"It is possible that children born by Caesarean section differ from other children with respect to some unknown characteristic which consequently increases their risk of diabetes, but it is also possible that Caesarean section itself is responsible," said author Dr. Chris Cardwell.

He said there may be some reason the delivery causes the immune system to attack insulin-producing cells.