“Previous research has linked a mother’s obesity to her child’s risk for autism, but these studies didn’t take into account the father’s weight. This may have overestimated the mother’s role in the risk of autism,” said the researchers.
In fact, the new study dropped the autism risk linked to an obese mother from 17 percent to nine percent after factoring in the father’s weight.
For the study, researchers analyzed the medical records of nearly 93,000 children, including 419 diagnosed with autism spectrum disorders. The data was pulled from the Norwegian Mother and Child Cohort Study, in which researchers recruited pregnant women between 1999 and 2008 and followed their families through early childhood.
Researchers calculated the parents’ body mass index (BMI) through questionnaires given to the children’s mothers at 18 weeks of pregnancy. The findings showed that about 10 percent of mothers and fathers were obese, with a BMI of 30 or higher. A healthy BMI is between 18 and 25.
The study also examined risk for milder subtypes of autism, including pervasive developmental disorder-not otherwise specified (PDD-NOS) and asperger syndrome.
The risk varied among these subtypes: Obese men have a 73 percent increased risk and obese women have a 34 percent increased risk of having a child with classic autism compared with healthy-weight parents. For Asperger syndrome, obese men are at double the risk and obese women are at a 40 percent increased risk.
As the father’s weight increases, so does his child’s risk for autism and Asperger syndrome. Obesity in either parent is not associated with an increased risk of PDD-NOS.
The researchers also factored in the parents’ medical issues and lifestyle that could have affected their children’s autism risk. According to the data, obese mothers and fathers are less educated and smoke more than do parents with a healthy BMI.
Obese mothers were also less likely to have taken folic acid supplements before becoming pregnant compared to women of a healthy weight. Research has previously found that women who take folic acid around the time of conception are less likely to have a child with autism.
Obese women also have a higher risk of preeclampsia — high blood pressure during pregnancy that can lead to seizures — as well as premature delivery. They are also more likely to have type II diabetes and gestational diabetes, which studies have shown may increase the risk of autism in the child.
“It is still unknown why a father’s weight might increase his child’s risk for autism. Genetics may play a role,” said the researchers. “For example, deletions on chromosome 16p11.2 are implicated in both autism and morbid obesity, and fathers may pass these on to their children.”