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Study: Infections During Pregnancy Do Not Cause Autism


A new study from Sweden suggests that infections in pregnant women do not cause neurodevelopmental conditions, such as autism, in children.

"Our results can reassure expectant parents by indicating that infections during pregnancy may not pose as great a risk to the baby's brain as previously thought," says Håkan Karlsson, a researcher at the Department of Neuroscience at Karolinska Institutet and the study's senior author.

The study published in the Lancet Psychiatry investigated whether there is a causal relationship between infections in the woman during pregnancy and autism or intellectual disability in the child.

Researchers examined data on 549 967 children born between 1987 and 2010 in Sweden. The study included only those severe infections that required specialist care and were identified using diagnostic codes from patient and birth records.

As in previous studies, researchers found infections that required care were linked to an increased risk of autism and intellectual disability in children.

However, when comparing sibling pairs where the mother had had an infection during one pregnancy but not the other, researchers could not find any link between infection and the children's risk of autism. For intellectual disability, the link was weaker when the researchers compared sibling pairs than when they compared children who are not related.

Researchers also found that infections during the year before pregnancy were linked to the risk of autism to the same degree as infections during pregnancy but not linked to the risk of intellectual disability.

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

Researchers do not rule out that infections during pregnancy may affect children's risk for intellectual disability. In any case, infections during pregnancy may not influence the risk of intellectual disability to the same extent as previously thought.

Study authors also emphasize that they have only looked at the diagnosis of infections in general. They say their findings "do not contradict the significance of the well-established links between some specific viral infections during pregnancy, such as cytomegalovirus infection and rubella, and the risk of serious developmental conditions in the child."

The researchers also point out that infections by the agent causing COVID-19 were not included in their study.

Causes are unknown

About 1 in 44 children has been identified with autism spectrum disorder (ASD), according to the Centers for Disease Control and Prevention (CDC). The condition is more than four times more common among boys than girls.

Autism usually appears before the age of 3. It impacts the normal development of the brain in the areas of social interaction, communication skills, and cognitive function.

The exact cause of autism is unknown. Research suggests that the condition develops from a combination of genetic and nongenetic, or environmental, influences.

According to the CDC, the risk factors for autism can include having a sibling with ASD, having certain genetic or chromosomal conditions, such as fragile X syndrome or tuberous sclerosis, experiencing complications at birth, and being born to older parents. Pregnancies spaced less than one year apart also increase the risk of autism.

Resources:

Karolinska Institutet. New knowledge about the link between infection during pregnancy and autism.

Lancet Psychiatry. Maternal infection during pregnancy and likelihood of autism and intellectual disability in children in Sweden: a negative control and sibling comparison cohort study.

CDC. Data & Statistics on Autism Spectrum Disorder.

National Autism Association. Autism Fact Sheet.

Autism Speaks. What Causes Autism?

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