Prospective parents naturally worry about the health of their baby. As a result of this, the researcher behind the new study believes it’s necessary to point out the possible sources of error in her findings, which show that influenza may increase the risk of having a child with autism. (Photo: Colourbox)

Influenza may increase the risk of infantile autism

New study shows that influenza or prolonged periods of fever during pregnancy may increase the risk of having a child with infantile autism. Read why the researcher behind the study advises pregnant women NOT to worry.

Children born with severe autism usually face a life filled with difficulties for themselves and their parents.

The children can, for instance, react violently to entirely normal sense impressions, experience sleeping problems and display self-harming behaviours.

So it comes as no surprise that expectant mothers often worry that their child may be born with this rare disorder.

A new Danish study now reveals a link between influenza and fever episodes lasting more than a week during pregnancy and infantile autism.

If I were pregnant and read about this, I wouldn’t get vaccinated against the flu or worry unduly.

Hjördis Osk Atladóttir

The study has been cited by media all over the world, but the study’s lead author tells ScienceNordic that due to methodological limitations of the study, the new findings shouldn’t be regarded as a cause for worry:

“If I were pregnant, I wouldn’t get vaccinated against the flu or worry unduly,” says Hjördis Osk Atladóttir, MD, PhD, of Aarhus University’s Department of Public Health, who was the lead author of the new study, published in the journal Pediatrics.

Almost 100,000 women examined

The researchers examined data from the Danish National Birth Cohort, which enrolled 101,033 pregnant women from the period 1997-2003, in which about 97,000 children were born.

The women were asked to fill in a questionnaire, which included information about whether or not the women had suffered from influenza or episodes of fever during their pregnancy.

There will always be a statistical uncertainty, and in this study we cannot exclude the possibility that our results are random.

Hjördis Osk Atladóttir

Information about autism diagnoses was found in national registers. The figures then underwent statistical analysis.

There were 808 out of the 97,000 mothers that claimed they had experienced influenza during pregnancy. Out of these 808, seven had given birth to a child with infantile autism.

The study found that mothers suffering from influenza in the first or second trimester of their pregnancy were 2.3 times more likely than normal to give birth to a child with autism.

Researcher: no cause for worry

The study should not give pregnant women any reason to worry about catching the flu while their stomach is growing, insists Atladóttir.

”Our study shows that 99 percent of women who experience influenza, fever, or take antibiotics during their pregnancy do not give birth to children with autism.”

Less than one percent of the women experiencing influenza had a baby with this rare disorder. The increased risk of 2.3 should be viewed in relation to the fact that 0.4 percent of all infants in the population are born with infantile autism. When you multiply 0.4 with 2.3, the occurrence of infantile autism is still below 1 percent.

American researcher baffled by cautious conclusion

In an article on LiveScience, a US scientists says that he doesn’t understand Atladóttir’s cautious conclusions of the study.

“The data in the study indicates that a flu infection in the mother or a prolonged fever doubles the risk of autism in children,” says biologist Paul H. Patterson, of the California Institute of Technology, whose research interests include the link between infections and the development of the human brain.

The LiveScience article also emphasizes that a study from May 2012 shows a similar result in terms of the correlation between prolonged fever in the pregnant woman and autism in her child.

Rare disorder and statistical uncertainty

Atladóttir explains that the correlation in the study from May only applies to prolonged fever and not the flu. She describes her study as a speculative study:

“There will always be a statistical uncertainty, and in this study we cannot exclude the possibility that our results are random,” she says. “Firstly, our data is not flawless as the women may have given wrong answers in the questionnaires. Secondly, we have made a lot of analyses – 106 analyses in total. We cannot exclude the possibility that the positive results obtained in some of these analyses are random.”

The researcher adds that infantile autism is an extremely rare disorder. A doubling of these figures, she says, does not increase the risk of giving birth to a baby with infantile autism to a sufficiently high degree that pregnant woman need to worry about it.

She does, however, stress that her study has academic merit, since it can be used by other researchers to conduct further studies about possible links between influenza, fever and the use of antibiotics during pregnancy and the development of infantile autism.


Read the Danish version of this article at

Translated by: Dann Vinther

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