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More Evidence That Fevers During Pregnancy May Increase Autism Risk

Fevers during pregnancy—especially in the second trimester—may be linked to autism in children, a new study suggests. Mothers who had fevers during their second trimesters were 40 percent more likely to have children with autism, researchers found, while mothers who had three or more fevers after during their twelfth week of pregnancy were at even higher risk. But as convincing (and scary) as those numbers may seem, many experts remain unconvinced.

“The reason for the association could relate to a specific infection, immune responses, or even how the fever is treated,” Lonnie Zwaigenbaum, co-director of the Autism Research Centre at the University of Alberta who was not involved in the study, told Fatherly. “It is even conceivable that a tendency to seek medical attention for concerns regarding early behavioral concerns may be associated with greater reporting of fever symptoms during pregnancy.”

Mady Hornig, coauthor on the study from Columbia University, agrees that the findings are less of a cause for alarm and more of an additional piece within an increasingly complex puzzle. “Fevers are common and autism is still relatively rare,” she says. “Not every mother who has a fever, even in the second trimester, will have an increased risk.”

Hornig and her team followed 95,754 children born between 1999 and 2009, via data obtained by through the Autism Birth Cohort (ABC) Study. Mothers of 15,701 (about 16 percent) reported fevers during their pregnancies. Overall, mothers who had fevers at any point during pregnancy were 34 percent more likely to give birth to children who would later be diagnosed with autism. Interestingly, mothers who took acetaminophen or Tylenol for their fevers did not decrease their risk. The researchers write that taking a NSAID medication, such as ibuprofen, could prove more effective than Tylenol but this is purely speculative at present, as none of the children of mothers who took ibuprofen for fever were diagnosed with autism, and overall numbers of women taking ibuprofen for fever were low.

While not involved in this study, Ousseny Zerbo, post-doc at the Vaccine Study Center at Kaiser Permanente Northern California Division of Research, told Fatherly that he has previously studied the potential link between autism and mothers who contract the flu during pregnancy. Zerbo says that Hornig and colleagues did solid work, but cautions that the findings are limited to self-reporting, and that mothers of autistic children may be more likely to recall past fevers in the first place. He also suspects that it is not the fever itself that increases autism risk, but the immune response that fevers tend to kick-off. “In animal studies we’ve found that even in absence of fever, just by stimulating the immune response you get the same results,” Zerbo says. “That tells me it’s not the infection but the reaction.”

Regardless, Zwaigenbaum, Zerbo, and Hornig all agree that the vast majority of the women who report fevers during pregnancy do not have children with autism, and that expectant parents should not freak out at the first sign of a fever. “We’re far from any medical or public health implications,”Hornig says. “What we have are implications for research.”