Study tentatively links flu in pregnancy and autism

Kids whose mothers had the flu while pregnant were slightly more likely to be diagnosed with "infantile autism" before age three in a new Danish study. But the children's overall risk for the developmental disorder was not higher than that of other kids.

Researchers said it's possible that activation of a mother's immune system - such as by infection with the influenza virus - could affect a fetus's developing brain. But they urged caution with the new findings, especially because of statistical limitations in their number-crunching.

"I really want to emphasize that this is not something you should worry about," said lead author Dr. Hjordis Osk Atladottir, from the University of Aarhus.

"Ninety-nine percent of women with influenza do not have a child with autism," she told Reuters Health. "If it were me that was pregnant, I wouldn't do anything different from before, because our research is so early and exploratory."

Her team's data came from a study that originally recruited more than 100,000 pregnant women in Denmark between 1996 and 2002. The women were called multiple times during their pregnancies, and once afterward, to ask about any new infections they had or medications they had taken.

The new report includes 96,736 kids born from that initial cohort who were between 8 and 14 years old at the time of the analysis.

Using a country-wide register of psychiatric diagnoses, Atladottir and her colleagues found that 1 percent of all kids were diagnosed with autism, including 0.4 percent with infantile autism - in which the main symptoms all show up before age three.

There was no link between a range of infections in pregnancy - including herpes, coughs and colds and cystitis - and the chance a baby would develop autism or infantile autism, according to the report published Monday in Pediatrics.

And among 808 women who reported having the flu while pregnant, there was no increased risk of autism in their children. However, seven of those babies, or 0.87 percent, were diagnosed with infantile autism, compared to the rate of 0.4 percent among kids in general.

There was also an increased - albeit sometimes borderline - risk of both autism and infantile autism in babies of women who had fevers for a week or more during pregnancy, as well as mothers who took some types of antibiotics.

Atladottir said there is some research in rodents suggesting women's activated immune cells can cross the placenta and affect chemicals in a fetus's brain. But how those findings apply to humans is still a question mark.

"It's all very unsure now - we don't really know anything," she said.

In the United States, about one in 88 children is now diagnosed with autism or a related disorder.

One limitation of the new study, the researchers noted, is that they did 106 statistical tests comparing the risk of autism or infantile autism with various infections and drugs.