New knowledge about the link between infection during pregnancy and autism

Credit: Mart Production

Infections in pregnant women have been linked to increased risk of neuropsychiatric conditions, such as autism, in the child later in life. But it does not appear to be the infections themselves that cause autism, researchers from Karolinska Institutet show in a study published in The Lancet Psychiatry.

Our results can reassure future parents by showing that infections during pregnancy may not pose as much risk to the child's brain as previously thought, say Håkan Karlsson, researchers at Department of Neuroscience at Karolinska Institutet and the study's last author.

Previous studies have shown a link between infections of the future mother during pregnancy and increased risk of autism and intellectual disability in the child later in life.

But they have not been able to say whether it is really the infection of the mother that is the cause, or whether other factors are behind it. Researchers from Karolinska Institutet have now studied this more closely.

Over 500,000 children studied

Håkan Karlsson,
researcher at the Department of Neuroscience,
Karolinska Institutet.
Photo credit: Ulf Sirborn

The current study is based on data on more than 500,000 children born in 1987 to 2010. The purpose was to investigate where there is a causal link between infections in the woman during pregnancy and autism or intellectual disability in the child. Infections were landed if they were serious enough to require specialist care and they were identified using diagnostic codes in the patient and birth register.

As in previous studies, the researchers saw that infections require specialist care during pregnancy were linked to an increased risk of autism and intellectual disability in children.

But when the researchers studied siblings, the result was different. In comparisons between siblings where the mother had an infection during one pregnancy but not the other, they could not find any link between infection and the children's risk of autism. For intellectual disabilities, the connection was weak when the researchers compared siblings than when they compared children who are not related.

The researchers also investigated the risk of autism and intellectual disability in children where the mother had been diagnosed with a serious infection this year before pregnancy. The idea was that an infection before pregnancy would not be linked to increased risk of autism and intellectual disability if it really was the infection during pregnancy that causes the conditions.

In this analysis, the researchers saw that infections during the year before pregnancy were linked to the risk of autism as much as infections during pregnancy, but not linked to the risk of intellectual disability.

Other environmental factors and genetics

Martin Brynge, PhD student
 at the Department of Global Public Health,
Karolinska Institutet
Photo credit: Ulf Sirborn

The link between infections in pregnant women and the increased risk of autism in their children does not appear to be a causal link. Our results suggest that the risk increase is more likely to be explained by factors common between family members, such as genetic variation or certain aspects of the shared environment, say Martin Brynge, doctoral student at Department of Global Public Health, Karolinska Institutet, and one of the study's first two authors.

Since the results were less clear for intellectual disabilities, it cannot be cleared out that infections during pregnancy can affect that risk, but in that case not as much as previously thought, according to KI researchers.

The researchers emphasize that they have only looked at infection diagnoses in general. The study does not contradict the importance of the well-established links between certain specific viral infections during pregnancy, such as cytomegalovirus infection and rubella, and the risk of serious developmental conditions in the child. The study was done before the covid-19 pandemic and therefore does not include SARS-Cov-2 infections. It is still important for pregnant women to follow their midwife's advice on infection control.

The research has been funded by the Swedish Research Council, the Stanley Medical Research Institute and Autism Speaks. The researchers do not report any potential conflicts of interest.

Source/Credit: Karolinska Institutet

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