Kids are at higher risk for autism if either — or both — of their parents are over age 35 at the time of birth, new research suggests.

In a study of more than 9,500 Danish children diagnosed with autism, researchers found that children were up to 28 percent more likely to have the developmental disorder if their father was over 35. The odds increased to as much as 55 percent for dads over 40.

Meanwhile, autism odds rose 21 to 37 percent when moms were over 35 and increased to as high as 65 percent for mothers over 40, according to the study published in the journal Annals of Epidemiology late last month.

However, a child’s odds of autism did not appear to be heightened further if both parents were older, the researchers said.

Why older parents are more likely to give birth to children with autism remains unclear. Those behind the study say they’re looking to expand their study sample by analyzing data on children from an additional five countries, reports Reuters. To read more click here.

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