A large Swedish study of 3.7 million people has found that rare infections passed from a pregnant woman to the fetus are linked to much higher risks of autism and intellectual disability later in life. The findings were published in JAMA Pediatrics. The research focused on a group of infections known as TORCH, which includes cytomegalovirus, rubella, toxoplasma and herpesvirus.
Kids born with a TORCH infection had roughly three times the chance of being diagnosed with autism. They also had over seven times the odds of having an intellectual disability, and they were up to 30 times more likely to suffer from severe to profound intellectual disability.
What the TORCH Group Covers
These infections are a group of rare conditions where certain germs can get past the placenta and affect a developing fetus. Usually, most common infections do not directly reach a developing fetus, but these particular pathogens can sometimes pass through the placenta and lead to a congenital infection.
According to the researchers, the infections make up a tiny fraction of all autism cases in the general population. Yet for the children who do get the condition, the odds of developing it are noticeably higher.
The Study’s Scale
The researchers examined health and education records for 3.7 million people born in Sweden between 1987 and 2021. Among this population, 975 people had been diagnosed with a congenital TORCH infection.
The researchers tracked participants for up to three decades, which gave them the time needed to determine whether these infections were linked to later neurodevelopmental diagnoses and educational results.
This research draws on national register data encompassing nearly the whole population of Sweden, making it the biggest undertaking yet in this field.
The Numbers Behind the Link
The relative risk increase is notable, yet congenital TORCH infections are uncommon, which means they make up only a small share of autism and intellectual disability cases throughout the population.
About 1.2 percent of severe intellectual disability cases in Sweden may stem from congenital TORCH infections, according to the researchers’ estimates. The same researchers also put the proportion of autism cases attributable to such infections at around 0.034 percent.
The researchers estimate that at the individual level, roughly one in five children born with a TORCH infection may go on to develop autism.
Checking Against Family Traits
To see if family traits could explain the results instead, the team turned to sibling comparisons. They pitted children who had been exposed to a TORCH infection against their own brothers and sisters who had not.
These comparisons kept a consistent pattern, which suggests that common family influences by themselves fail to fully account for the connections.
No clear connections were found by the researchers between congenital TORCH infections and other neuropsychiatric conditions, including ADHD or obsessive-compulsive disorder.
School Performance and Grades
Among children who did not receive a diagnosis of autism or an intellectual disability, those who had a congenital TORCH infection scored lower grades on average compared to children who did not have such an infection.
According to the researchers, their results underscore how crucial it is to stop infections from being passed on to a developing fetus while a woman is pregnant.
Rubella as a Model Case
Sweden’s national vaccination programs have all but eliminated rubella, an illness whose prevention has shown what a major difference it can make.
The scientists say keeping vaccination programs and other preventive measures in place is still key to cutting down on infections that can move from a pregnant woman to her developing fetus.
The Broader Picture
The research was financed by the Swedish Research Council. A co-author, David Mataix-Cols, reports earning author’s fees from UpToDate Inc and being a partner in Scandinavian E-Health AB, which bears no relation to the publication.
| Condition | Relative Risk Increase |
|---|---|
| Autism | About three times higher |
| Intellectual Disability | More than seven times higher |
| Severe to Profound Intellectual Disability | Up to 30 times higher |
What the Researchers Said
“It is important to emphasize that it is unusual for these infections to be transmitted from mother to child. They account for a very small proportion of all cases of autism in the population, but for those children who are actually affected, we see a clearly elevated risk of both autism and intellectual disability,” says Reneé Gardner, a researcher at the Department of Global Public Health at Karolinska Institutet, who contributed to the study.
A PhD student and lead author of the study is credited with the statement, according to “It has long been known that these infections can cause intellectual disability. However, the link to autism has been less clear in previous research, which has often been based on small patient groups. This study is the largest to date in this field and is based on national register data covering almost the entire population of Sweden,”.
The name being given is Reneé Gardner, according to “Our results suggest that certain infections transmitted to the fetus during pregnancy may have long-term effects on brain development. Although these congenital infections are rare, some of them can be prevented, which makes them important from a public health perspective,”.
The Takeaway
The research establishes a direct connection between these uncommon infections and significant developmental results. The findings do not come across as alarming, however.
While these infections rarely occur, they are not behind most cases of autism. The danger to families is genuine: around one in five children born with a TORCH infection may go on to develop autism.
The study offers a practical takeaway: rubella has nearly disappeared in Sweden because of vaccination, and it hints that other TORCH infections might go the same way if prevention efforts stay strong.
The results serve as a caution to pregnant women regarding the dangers these infections pose. It is uncertain whether enough women will take heed of it.
Source material: “Rare pregnancy infections may triple the risk of autism,” ScienceDaily.
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