Perhaps the single biggest question among parents concerned about autism is what causes the developmental disorder, which now affects one in 88 children in the U.S.
A preliminary new study published Monday in the journal Pediatrics found that if a woman has the flu or a prolonged fever during her pregnancy, her child may be at increased risk for autism spectrum disorders. Researchers analyzed data from nearly 97,000 children born in Denmark between 1997 and 2003 and their mothers' reports on any infections they had while they were pregnant as well as whether they had taken antibiotics.
Common infections, including respiratory problems, colds and urinary tract infections, did not seem to be a major risk factor for autism, the study found. But children whose mothers said they had the flu during their pregnancy were twice as likely to be diagnosed with an ASD before they turned 3 years old. And children whose mothers had a prolonged episode of fever -- lasting a week or more -- were three times as likely to be diagnosed with an ASD.
"I want to emphasize that this really was an exploratory study," said Coleen Boyle, director of the National Center on Birth Defects and Developmental Disabilities with the Center for Disease Control and Prevention. Boyle was not a researcher on the study, but one of her colleagues at the CDC worked on it.
Studies in animals have found that when a woman's immune system is "triggered" during pregnancy in order to fight off infection, that may somehow influence a child's developing brain, Boyle told HuffPost. But the mechanisms are not yet understood.
The new study also linked antibiotic use during pregnancy to a slightly higher risk of autism, but the reason behind the link is unclear. According to the study's authors, the antibiotics themselves might have some sort of effect, but the underlying condition the medications are used to treat may also have an effect. Or it may simply be chance.
"It's intriguing, it's suggestive, but it's still is very preliminary," said Marshalyn Yeargin-Allsopp, chief of the developmental disabilities branch of the CDC.
In an email to The Huffington Post, Irva Hertz-Piciotto, a professor of public health sciences with the University of California Davis' MIND Institute, called the new study "noteworthy" and said it adds to a growing body of literature probing the possible link between maternal infection and autism. Hertz-Piciotto was a researcher on a study published last spring in the Journal of Autism and Developmental Disorders that found moms who had a fever during pregnancy were more than twice as likely to have a child with autism or a developmental delay than women who had no fever, or women who took medicine to reduce their fever.
But autism experts caution that research in this area is far from definitive and say that it should not frighten expectant mothers. The causes of autism remain a mystery and are likely a combination of many genetic and environmental factors -- meaning anything outside of the body that can influence health.
"Most women experiencing flu or fever or those taking antibiotics did not have children with an autism spectrum disorder," Boyle stressed. She listed simple steps women can take to help ensure a healthy pregnancy: wash their hands frequently to prevent infection, call their doctors right away if they have a fever or flu-like symptoms, and get a flu shot.
The Centers for Disease Control and Prevention recommends a flu shot for everyone who is at least six months old, and includes pregnant women on its list of people for whom vaccination is particularly important.