Prior studies have shown that maternal obesity during pregnancy may increase the risk of developmental disorders in the child. However, a recent study shows that paternal obesity could be a greater factor than maternal obesity.

"We have a long way to go. We must study genetic factors in the relationship between obesity and autism, as well as environmental factors associated with switching the genes on or off -- so-called epigenetic factors,"  Dr. Pål Surén, a researcher from the Norwegian Institute of Public Health, said in a statement.

For the study, researchers used data from the Norwegian Mother and Child Cohort Study. They studied questionnaire data from more than 90,000 Norwegian children at three, five and seven years of age.

They found that 419 children, or approximately 0.45 percent, had an autism spectrum diagnosis. Of the study participants, they found that 22 percent of the mothers and 43 percent of the fathers were overweight with a body mass index of between 25 and 30. Approximately 10 per cent of mothers and fathers were obese, with a BMI of 30 or more.

Based on their findings, researchers determined that maternal obesity ha little association with the development of autism in the child. However, they found a doubled risk for development of autism and Asperger's syndrome in the child if the father was obese, compared with a normal weight father.

"We were very surprised by these findings because we expected that maternal obesity would be the main risk factor for the development of autism spectrum disorder.  It means that we have had too much focus on the mother and too little on the father," Suren said. "This probably reflects the fact that we have given greater focus to conditions in pregnancy, such as the growth environment for the fetus in the womb than both environmental and genetic factors before conception."

Researchers said their findings suggest that there may be a genetic link between obesity in the father and the development of autism spectrum disorder in the child.

The findings were recently published in the journal Pediatrics.