In a study of nearly 100,000 Norwegian children, those whose mothers reported having a fever or two at some point during their pregnancy were 1.3 times more likely to be diagnosed with autism spectrum disorder, according to a report published Tuesday in Molecular Psychiatry. Medical News Today reports approximately 1.5% of US children have ASD. But the study found the rate was closer to 3.7% for children whose mothers had a fever during pregnancy, the Washington Post reports.. The timing and number of fevers appear to play a part. According to a press release, a fever in the second trimester raised the odds of ASD by 40%; three or more fevers after the 12th week of pregnancy raised them by 300%.
The study out of Columbia University gives more credence to a theory that infectious agents lead to immune responses in pregnant women, which in turn lead to issues with brain development in their fetuses. Researchers say it's not the initial infection but the fever response that impacts brain development, possibly through molecules created by the woman's immune system making their way into the fetus' neurological system. Interestingly, the study found no cases of ASD among the children of mothers who took ibuprofen for their fevers during pregnancy. However, there were too few women in the study who reported taking ibuprofen to say anything for sure. (New hope for diagnosing autism in babies.)