Rare Infections During Pregnancy Are Linked to Autism and Intellectual Disability

Most infections a pregnant woman catches never reach her baby. A small group of pathogens, however, can slip across the placenta and infect the foetus directly. A new study from Sweden’s Karolinska Institutet, published in JAMA Pediatrics, shows that when this does happen, the consequences for the child’s brain development can last a lifetime.

What are TORCH infections?

TORCH is an acronym for a group of infections that can be passed from mother to foetus: Toxoplasmosis, Other (including syphilis), Rubella, Cytomegalovirus (CMV) and Herpes simplex virus. Unlike most everyday infections, these agents can cross the placental barrier. It has long been known that they can cause intellectual disability, but their relationship to autism has been much less clear, largely because earlier studies were small.

Three decades of national data

The researchers used Swedish national registers covering 3.7 million people born between 1987 and 2021. Of these, 975 had been diagnosed with a congenital TORCH infection. Participants were followed for up to 30 years to see who later received an autism or intellectual disability diagnosis, and how they fared at school. It is the largest study of its kind to date.

What they found

·         Children with a congenital TORCH infection were roughly three times more likely to be diagnosed with autism.

·         Their likelihood of an intellectual disability diagnosis was more than seven times higher, and the risk of severe to profound intellectual disability was up to 30 times higher.

·         The team estimates that around one in five children born with a TORCH infection may go on to develop autism.

·         No clear links emerged with other neuropsychiatric conditions such as ADHD or obsessive-compulsive disorder.

·         Even children without an autism or intellectual disability diagnosis had somewhat lower school grades on average than peers who were not infected.

Is it the infection, or the family?

A fair question with any observational study is whether something else, such as genetics or the home environment, explains the pattern. To test this, the researchers compared children who had a TORCH infection with their own siblings who did not. The results were similar, which suggests the associations cannot be explained solely by factors shared within families.

Big relative risk, small population impact

It is important to keep the numbers in perspective. Congenital TORCH infections are rare, so despite the high relative risks, they account for very little of the overall picture. The authors estimate that they are linked to about 1.2% of all cases of severe intellectual disability in Sweden and only about 0.034% of autism cases. As study contributor Reneé Gardner stresses, transmission from mother to child is unusual, but for the children affected the elevated risk is clear.

Why it matters: prevention

The encouraging part is that several of these infections can be prevented. Rubella, for example, has virtually disappeared in Sweden since national vaccination programmes were introduced, which the researchers see as a strong argument for keeping those programmes going. The Karolinska team also outlines practical measures for each TORCH group:

·         Toxoplasma: avoid raw or undercooked meat, wash vegetables well, and take care when handling cat faeces.

·         Other (e.g. syphilis): screening during pregnancy and antibiotic treatment.

·         Rubella: vaccination (MMR) before pregnancy.

·         Cytomegalovirus: good hand hygiene, and avoiding contact with young children’s saliva and urine.

·         Herpes simplex: identifying and treating infection during pregnancy; a caesarean section is sometimes performed if genital herpes is active before delivery.

The takeaway

This study does not suggest that infections explain autism in general; the vast majority of autism cases have no connection to TORCH infections. What it does show is that certain infections passed to the foetus can leave long-term marks on brain development, and that vaccination, screening and simple hygiene measures during pregnancy are worthwhile public health tools. The research was funded by the Swedish Research Council.

News release: Karolinska Institutet

Original paper: Sjöqvist H, Dalman C, Mataix-Cols D, Gardner RM, Karlsson H. “Congenital TORCH infections and neurodevelopmental outcomes: A population- and sibling-based cohort study.” JAMA Pediatrics, 2026. https://doi.org/10.1001/jamapediatrics.2026.4229 

Source: Rare Infections During Pregnancy Are Linked to Autism and Intellectual Disability