Infections caught in the womb tripled a child’s odds of autism across 3.7 million births

Children born with a congenital TORCH infection were about three times as likely to be diagnosed with autism as other Swedish children, in a registry study covering 3.7 million births between 1987 and 2021. The infections, caught from the mother before birth, were also tied to a more than sevenfold higher rate of intellectual disability. A team at Karolinska Institutet in Stockholm published the analysis in JAMA Pediatrics on September 21, 2026.

The tripled risk applies to a very small group. Only 975 people in the entire cohort had a clinically diagnosed congenital TORCH infection, and the researchers estimate those infections explain roughly 0.034% of autism cases in Sweden.

Swedish registers and the 975 infected children

The team linked national health, diagnosis and school records for everyone born in Sweden across 34 years and followed them for up to three decades. TORCH is shorthand for a group of infections that can cross the placenta: toxoplasmosis, rubella, cytomegalovirus and herpes simplex, with syphilis and other agents sometimes added. Hugo Sjöqvist, the doctoral researcher who led the work, described it as the largest study of its kind and based on register data covering almost the entire Swedish population, in the Karolinska news release.

The hazard ratio for autism was 3.10 across the cohort, according to a summary of the paper’s results. For intellectual disability it was 7.22, and for severe to profound intellectual disability it climbed to 23.51, which fits the up to thirtyfold figure in the university’s description. Roughly one in five children born with a TORCH infection went on to receive an autism diagnosis.

Sibling comparisons and the family-factor question

Why would an infection before birth show up years later as a diagnosis? The usual idea is that a pathogen, or the mother’s immune response to it, disturbs the developing brain during a window when circuits are forming. Cytomegalovirus is the best-studied example, and it can damage hearing and brain tissue in newborns. The register design cannot show the mechanism, only how strongly the exposure and the outcomes track each other, which is why the sibling comparison carries so much weight in the paper. Because Sweden records diagnoses in national registers from birth, nearly every child with a recorded infection could be followed into adulthood without relying on parents to recall events or on families volunteering to take part.

A raw comparison between infected and uninfected children could simply reflect families, genes or the health of the mother. The researchers addressed that by comparing siblings in the same family, one infected and one not. The autism hazard ratio held at 3.19 in that analysis, and the intellectual disability ratio rose to 11.28, so shared family background is unlikely to explain the pattern.

Autism with intellectual disability showed a ratio of 6.23, against 1.97 for autism alone, a gap that suggests the infections tilt development toward the more disabling end of the spectrum. Academic performance at age 16 was also lower by about 1.5 grade points. The ScienceDaily report on the study carries the same headline figures.

Rare exposure, limited reach and the case for prevention

Reneé Gardner of Karolinska’s Department of Global Public Health, a co-author, put the proportions plainly. She said it is unusual for these infections to be transmitted from mother to child and that they account for a very small proportion of all autism cases, yet affected children show a clearly elevated risk of both autism and intellectual disability, as Neuroscience News relayed. Christina Dalman, David Mataix-Cols and Håkan Karlsson are also named authors.

Absolute risk stays modest. About four in five infected children in the cohort did not receive an autism diagnosis.

The study has limits its authors acknowledge. It counts only symptomatic, clinically diagnosed infections, so milder ones that nobody recognised are missing. There was no routine newborn screening data and no information on treatment, and diagnostic coding can vary by period. Pregnancy complications may account for part of the outcome. The design shows association, and it does not isolate the virus or parasite as the cause.

The prevention message is concrete, and it is the part of the work with the clearest route to benefit, because several of these infections can be reduced by vaccination, hygiene advice in pregnancy, screening and treatment, long before any question about autism arises. The researchers point to rubella, which has been close to eliminated in Sweden by vaccination, as the model, and recommend the standard measures for each infection, with cytomegalovirus a particular target. The full results are in JAMA Pediatrics. The figure to watch is the 975: a group that small yields wide uncertainty in any subgroup, and replication in another national register would show how well the threefold figure travels.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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