Having a fever or flu in pregnancy may be linked with the development of autism in children, a new study suggests. While researchers are hesitant to draw strong conclusions, the study is at least the second showing such a link.

The researchers followed mothers in Denmark and the nearly 97,000 children they had between 1997 and 2003. During the study, 976 children in the study were diagnosed with autism.

Children were more likely to be diagnosed with autism if their mothers had the flu or developed a prolonged fever during the first or second trimester of pregnancy.

But the topic needs further study before stronger conclusions can be drawn, said study researcher Hjördis Osk Atladottir, of the University of Aarhus.

“Around 99 percent of women experiencing influenza, fever or taking antibiotics during pregnancy do NOT have children with autism,” Atladottir wrote to MyHealthNewsDaily in an email.

Dr. Marshalyn Yeargin-Allsopp, chief of the Centers for Disease Control and Prevention Developmental Disabilities Branch, who was not involved in the study, said, “We're not recommending clinically that physicians change their management of pregnant women based on these findings.”

One reason for the caution may be that pregnant women who are concerned about lowering their child's risk of autismwould, for the most part, simply need to adhere to existing guidelines, which recommend getting a flu shot, and treating fevers by taking acetaminophen and contacting their physician.

Some researchers were puzzled by the authors' caution.

“The data indicates that maternal flu infection or an extended fever increases the risk for autism in the offspring — a twofold increase,” said Paul H. Patterson, a biology professor who researches the connections between infection and neurological development at the California Institute of Technology.

Noting that the new finding is consistent with other research, Patterson said, “I'm not clear on why they appear to soft-pedal their results in their conclusions.”

A study published in May from researchers at the University of California, Davis found a similar connection, showing that mothers of children with autism were more likely to have had a prolonged fever in the late first or second trimesters of pregnancy, compared with mothers of children who didn't have autism.

Irva Hertz-Picciotto, an author of the UC Davis findings, said while the reason that fevers or flu during pregnancy may be linked with autism are unclear, it's thought that inflammation may have an adverse effect on early brain development.

“I think there’s some growing evidence that perhaps inflammation in the wrong tissue at the wrong time could interfere with normal developmental processes,” Hertz-Picciotto said.

There is also evidence for a link between mothers who have inflammatory conditions such as diabetes and autism in children, but that link, too, has not been conclusively established, she said.

“There is some growing evidence that in neurodevelopment, this could be part of a pathologic process, this could lead to behavioral type syndromes,” Hertz-Picciotto said.

Indeed, researchers are just beginning to develop an understanding of autism's causes, the experts said.

“We know a lot more than we knew five years ago, but the science is really in its infancy,” said Coleen Boyle, of the CDC.

A CDC-sponsored study, called the Study to Explore Early Development (SEED), is following more than 2,700 children in California, Colorado, Georgia, Maryland, North Carolina and Pennsylvania, with the hope of identifying factors that might influence autism spectrum disorders.

Boyle said that the possible environmental causes of autism can be more challenging to research than the disorder's genetic causes. For example, data in the new study had to be collected starting in the late 1990s.

“You can just see the time that's required to collect that kind of information,” Boyle said.

“There's not a lot of people looking at these environmental factors,” Hertz-Picciotto said. “This is something people should be paying more attention to, because it's actionable.”

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