Swedish study links prenatal infections to increased autism and intellectual disability risk

A large-scale Swedish study finds that rare infections passed from mother to unborn child significantly raise the risk of autism and intellectual disability, highlighting the importance of vaccination and infection prevention during pregnancy.

A large Swedish study has linked rare infections that can pass from a pregnant woman to her unborn child with a higher later risk of autism and intellectual disability, adding to evidence that some prenatal infections can have long-term effects on brain development. The research, led by Karolinska Institutet and published in JAMA Pediatrics, examined congenital TORCH infections, a group that includes cytomegalovirus, rubella, toxoplasma and herpesvirus. According to the investigators, these infections are uncommon, but when they do occur the consequences for affected children can be serious.

The team analysed health and education records for 3.7 million people born in Sweden between 1987 and 2021. Among them, 975 had a diagnosed congenital TORCH infection. Children in that group were about three times more likely to receive an autism diagnosis later in life than those without such an infection, and more than seven times more likely to be diagnosed with intellectual disability. For severe to profound intellectual disability, the increase in risk was much larger.

Although the relative risks were striking, the researchers stressed that the infections themselves are rare, so they account for only a small share of overall cases. They estimated that congenital TORCH infections may be linked to about 1.2% of severe intellectual disability cases in Sweden and roughly 0.034% of autism cases. Even so, among children born with a TORCH infection, the researchers estimated that around one in five may later be diagnosed with autism. The study also found no clear link with other neuropsychiatric conditions such as attention deficit hyperactivity disorder or obsessive compulsive disorder.

To test whether family background might explain the findings, the researchers compared affected children with their own siblings who had not had a congenital TORCH infection. The association remained broadly similar, suggesting that shared family factors alone are unlikely to account for the results. The study also found that, even among children without autism or intellectual disability, those with a congenital TORCH infection tended to have lower school grades on average.

Reneé Gardner of Karolinska Institutet said the findings highlight the importance of preventing infections that can be transmitted during pregnancy, while noting that it is unusual for these infections to pass from mother to child. Hugo Sjöqvist, the study’s lead author, said the work is the largest of its kind and is based on national register data covering almost the whole Swedish population. The researchers pointed to rubella as a reminder of what prevention can achieve: it has virtually disappeared in Sweden since the introduction of national vaccination programmes, underlining the public health value of maintaining protection against infections that can reach the fetus.