Large Swedish Study Finds Strong Association With Autism And Intellectual Disability
Rare infections that can pass from a pregnant woman to her developing fetus may be associated with substantially higher risks of autism and intellectual disability later in childhood, according to a large Swedish study published in JAMA Pediatrics.
Researchers from the Karolinska Institutet analysed health and education records of approximately 3.7 million people born in Sweden between 1987 and 2021. Among them, 975 had been diagnosed with a congenital TORCH infection.
The findings provide new evidence about how certain infections occurring before birth may be associated with later neurodevelopmental outcomes.
What Are TORCH Infections?
TORCH refers to a group of infections that can cross the placenta and infect a developing fetus.
The group includes infections such as:
• Toxoplasmosis
• Syphilis
• Rubella
• Cytomegalovirus
• Herpes simplex virus
These infections are relatively uncommon as congenital infections, but they can sometimes cause significant complications when transmitted from mother to fetus.
Autism Risk Was About Three Times Higher
Children diagnosed with a congenital TORCH infection were approximately three times more likely to later receive an autism diagnosis compared with children without such an infection.
The researchers also found an even stronger association with intellectual disability. Children with congenital TORCH infections were more than seven times as likely to receive an intellectual disability diagnosis.
For severe to profound intellectual disability, the reported increase was substantially larger, reaching as high as 30 fold in the study analysis.
The Infections Are Extremely Rare
The large relative differences need to be interpreted alongside the rarity of congenital TORCH infections.
The study included millions of births, but only 975 people were identified as having a congenital TORCH infection.
Researchers estimated that these infections accounted for only a very small proportion of autism cases in the Swedish population, approximately 0.034%.
Therefore, the findings do not suggest that these infections explain autism in the general population.
A Large Population Study
One strength of the research was its size.
The investigators were able to follow people born over several decades using Swedish national health and education records.
This allowed them to examine outcomes well beyond infancy and compare children with congenital infections with those who did not have these infections.
The researchers also conducted sibling comparisons.
The association remained similar when children with congenital TORCH infections were compared with their own siblings who did not have such infections, suggesting that shared family factors alone were unlikely to explain the findings.
What About Children Without Autism?
The researchers also examined educational outcomes.
Even among children who did not receive an autism or intellectual disability diagnosis, those with congenital TORCH infections had somewhat lower school grades at age 16 on average than children without the infections.
This suggests that the potential effects of congenital infection may extend beyond formal neurodevelopmental diagnoses.
However, educational performance can be influenced by many factors, so this finding should also be interpreted cautiously.
Does This Mean The Infections Cause Autism?
Not necessarily.
The study identified an association, not definitive proof of causation.
Because the research was observational, researchers cannot establish from these data alone that congenital TORCH infection directly causes autism.
Other biological and environmental factors may contribute to the observed relationship, even though the sibling analysis helped address some potential sources of confounding.
Why The Findings Matter
Autism has a complex and multifactorial origin.
Genetic factors play an important role, while researchers continue to investigate how prenatal and early life environmental factors may influence neurodevelopment.
The new findings add congenital infections to an area that warrants further investigation.
They also reinforce the importance of preventing, detecting and appropriately managing infections during pregnancy.
Prevention Remains Important
The researchers emphasised that congenital TORCH infections are unusual.
Nevertheless, several infections included in the TORCH group are preventable or manageable through established public health and clinical measures.
Prenatal care can help identify certain infections and provide appropriate testing, treatment, counselling or preventive measures when indicated.
Vaccination also plays an important role in preventing some infections, such as rubella, although vaccination decisions during pregnancy need to follow established medical guidance.
What This Means For Expecting Parents
The findings should not create unnecessary anxiety.
Most pregnancies do not involve congenital TORCH infection, and the study does not suggest that routine pregnancy infections automatically increase a child’s autism risk.
The research specifically concerns rare infections transmitted to the fetus, rather than ordinary infections experienced during pregnancy.
Pregnant women should continue routine prenatal care and discuss any infection symptoms, exposure concerns or vaccination questions with their healthcare provider.
The Importance Of Early Developmental Monitoring
The study also highlights the value of monitoring children’s development after birth.
Children with known congenital infections may benefit from appropriate developmental follow up so that concerns involving communication, learning, behaviour or other developmental areas can be identified early.
Early recognition does not prevent autism, but it can help children and families access appropriate developmental support when needed.
A New Area For Research
The study raises several questions for future research.
Scientists will need to understand whether particular pathogens carry different neurodevelopmental risks, whether timing of infection during pregnancy matters, and which biological mechanisms could connect fetal infection with later brain development.
Further research may also clarify whether preventing specific congenital infections changes long term neurodevelopmental outcomes.
