Piling on kilos during pregnancy can lead to overweight children and might be contributing to rising obesity rates, research has suggested.

A study involving more than 40,000 women and their 91,000 offspring confirms the link between childhood and weight gain in pregnancy.

It also indicates that a mother’s weight gain directly affects the obesity risk of her children.

For each kilogram of weight gained by its mother during pregnancy, a child’s body mass index (BMI) at age 12 increased by 0.02kg/m2, the study found.

Children of mothers who put on the most weight had a BMI that was 0.43 higher, on average, than those whose mothers gained the least weight.

BMI measurements are obtained by dividing weight in kilograms by height in metres squared. A BMI of 18.5 to 24.9 is considered normal, 25 to 29.9 overweight and 30 and above is looked at as obese.

Previous research highlighting the same trend might have been swayed by shared influences affecting mother and child, such as socio-economic background and genes.

To ensure they focused only on the conditions during pregnancy, the US scientists looked at mothers with two or more children.

Birth records were matched to school reports that included every child’s body mass index (BMI) at the age of 12.

The study was conducted in Arkansas, where it is compulsory for all state school children to have their weight and height measured every other year.

Comparing siblings with the same home environment and distribution of obesity genes helped to isolate the effects of pregnancy weight gain.

Pregnancy presents an attractive target for obesity prevention programmes because women tend to be particularly motivated to change behaviour during this time

Lead researcher David Ludwig, director of the New Balance Foundation Obesity Prevention Centre at Boston Children’s Hospital, said: “From the public health perspective, excessive weight gain during pregnancy may have a potentially significant influence on the propagation of obesity.

“Pregnancy presents an attract-ive target for obesity prevention programmes because women tend to be particularly motivated to change behaviour at this time.”

Writing in the online journal Public Library of Science Medicine, the authors show how weight gain in pregnancy could further contribute to obesity on a national scale.

Children born to mothers with high pregnancy weight gain had an eight per cent increased risk of obesity.

This could account for “several hundred thousand annual cases of paediatric (childhood) overweight or obesity worldwide”, said the researchers.

They added: “The 0.43kg/m2 increase in BMI could represent a significant component of the estimated 2kg/m2 increase in mean childhood BMI in the US since the 1970s.”