"Our findings are interesting for research purposes, but they should not alarm women who are pregnant," says researcher Hjordis Osk Atladottir, MD, PhD, of Denmark’s University of Aarhus. "It needs to be emphasized that around 98% of the women in this study who experienced influenza or fever or took antibiotics during pregnancy did not have children with autism."
The study, published today in the journal Pediatrics, included children born in Denmark between 1997 and 2002, including those with a diagnosis of autism spectrum disorder.
Flu, Fever, and Autism
This was reassuring because these are some of the most common infections among pregnant women, Atladottir says.
But having the flu during pregnancy was linked to a twofold increase in a woman’s chance of having a child diagnosed with an autism spectrum disorder before the age of 3.
Children whose mothers reported having a fever lasting for more than a week had a threefold increase in autism risk.
Still, despite these increases, the overall risk remained low.
Does Infection Alter the Fetal Brain?
Animal studies suggest that fighting off infection during pregnancy can affect the developing fetal brain, says Coleen Boyle, PhD, who directs the CDC’s National Center on Birth Defects and Developmental Disabilities.
But she says it is not clear if fetal exposure to infection or fever plays any role -- even a small one -- in autism risk.
Boyle says flu is more likely to cause severe illness in pregnant women than in women who are not pregnant.
That is why the CDC and the American Congress of Obstetricians and Gynecologists recommend that pregnant women be especially vigilant about getting flu shots during flu season.
‘No Single Cause of Autism’
Pediatrics professor Susan L. Hyman, MD, of the University of Rochester Medical Center, says a major strength of the study was the reporting of illnesses during pregnancy and not years later after the children’s diagnosis was known.
Pediatrician Andrew Adesman, MD, says while the role of genetics in autism is beginning to be understood, the non-genetic contributors to the disorder mostly remain a mystery.
Adesman is chief of developmental and behavioral pediatrics at Steven & Alexandra Cohen Children’s Medical Center of New York.
"It is important to recognize that there is no single cause of autism," he says. "There are many different lines of research that are being pursued, and some will inevitably prove more fruitful than others."