A study, which covered over 129,000 mothers in Stockholm and their 189,000 children, found that mothers who were very obese, or with a body mass index of 35 or over, had a 61 per cent increased risk of their children developing asthma by the time they were between 8 and 10 years of age.

"We found that there was a clear increased risk of childhood asthma, medication use and hospitalisation with an increasing degree of obesity and overweight in mothers in early pregnancy," said lead author Adrian Lowe from the Murdoch Childrens Research Institute and University of Melbourne.

"Obese mothers had a 41 per cent increase in the odds compared to normal weight mothers ... those who were a little overweight had 18 per cent increased chance," Lowe said.

The study, which was conducted by both Australian institutes and Umea University in Sweden, was published in the Journal of Allergy and Clinical Immunology.

Lowe explained that maternal obesity increases the child's risk of obesity, which influences the infant's immune system and its responses toward allergies.