Overweight and obesity among women increases the risk of type 1 diabetes in their offspring but only if neither parent has diabetes, research shows.

The study of more than 1.2 million children born in Sweden between 1992 and 2004 found that having a mother who was obese during pregnancy (BMI≥30) was associated with an increase in risk of developing type 1 diabetes of a third, when compared with children of mothers whose BMI was in the normal range.

However this increased risk was found only in children of parents without diabetes. The risk of a child developing type 1 diabetes was increased by up to a fifth depending on whether the mother or father had type 1 or type 2 diabetes but this risk did not increase further with maternal obesity in pregnancy.

“This nationwide cohort study demonstrates that paternal and maternal diabetes and first trimester maternal obesity are associated with increased risks of type 1 diabetes in the offspring,” wrote the researchers in Diabetologia. 

“The finding that first trimester maternal obesity was a risk factor for type 1 diabetes only in offspring of parents without diabetes, and with no further increment in risk in offspring of parents with diabetes, clearly suggests that heredity for type 1 diabetes is the strongest risk factor of the two for development of type 1 diabetes in the next generation,” they said.

“Prevention of overweight and obesity in women of reproductive age may contribute to a decreased incidence of type 1 diabetes,” they concluded.