Certain rare infections that can pass from a pregnant woman to her developing baby may be associated with a significantly higher risk of autism and intellectual disability later in childhood, according to a large study from Sweden. Researchers examined health and education records involving approximately 3.7 million people born in Sweden between 1987 and 2021. Among them, 975 people had been diagnosed with a congenital infection from a group commonly referred to as TORCH infections. TORCH infections include toxoplasmosis, syphilis, rubella, cytomegalovirus and herpes simplex virus, along with several other infections that can potentially be transmitted from a mother to her fetus during pregnancy. The researchers found that people who had experienced a congenital TORCH infection were approximately three times more likely to be diagnosed with autism compared with those who had not experienced such an infection. They were also more than seven times more likely to have an intellectual disability. The risk was particularly elevated for severe forms of intellectual disability. Researchers reported that the relative risk for severe or profound intellectual disability could be substantially higher among people who had experienced a congenital infection.
Despite the large relative increase in risk, researchers emphasized that congenital TORCH infections are extremely uncommon. Because so few pregnancies are affected, the infections are estimated to account for only a very small proportion of autism cases across the overall population. This distinction is important. The study does not show that infections during pregnancy are a common cause of autism, nor does it mean that a pregnant woman who develops an infection will have a child with autism. The researchers specifically studied congenital infections, meaning infections that are transmitted to the fetus before birth. A routine infection during pregnancy that does not reach the developing baby is different and was not necessarily part of the study. The study also examined children’s educational outcomes. Researchers found that children who had experienced congenital TORCH infections tended to have lower academic performance during adolescence. Interestingly, some differences were observed even among children who did not have a formal diagnosis of autism or intellectual disability. To explore whether genetics or other family characteristics could explain the results, researchers conducted analyses involving siblings. The association between congenital infection and later autism or intellectual disability remained after accounting for factors shared within families. However, the researchers caution that the study was observational. This means it can identify an association between congenital infection and later developmental outcomes but cannot prove that the infection itself directly caused autism.
Scientists have been studying for years how infections and inflammation during pregnancy may affect fetal development. The developing brain is particularly sensitive during certain stages of pregnancy, and severe infections can sometimes interfere with normal neurological development. One possible explanation is that an infection may trigger an inflammatory response in the mother’s body or directly affect the developing fetus. Inflammation and immune-system activity can potentially influence how the fetal nervous system develops. Different infections may also affect pregnancy and fetal development in different ways. Some can cause problems with hearing, vision, brain development, growth or other organs. Cytomegalovirus, or CMV, is one of the most common congenital infections and can sometimes cause developmental problems or hearing loss. Many babies infected with CMV, however, have no obvious symptoms at birth.
Rubella can cause serious birth defects when a pregnant woman becomes infected, particularly early in pregnancy. Vaccination before pregnancy is an important way to prevent congenital rubella.
Toxoplasmosis can be transmitted to a fetus if a pregnant woman becomes infected with the parasite. Exposure can occur through undercooked meat, contaminated soil or contact with infected cat feces.
Syphilis can also cross the placenta and cause serious complications for a developing baby. Screening during pregnancy allows the infection to be detected and treated.
Herpes simplex virus can be transmitted from a mother to a newborn, with the greatest concern generally occurring around the time of delivery. Medical management can reduce the risk of transmission in appropriate circumstances.
The researchers say the findings highlight the importance of preventing, detecting and treating infections that can affect unborn babies.
For pregnant women, the findings do not suggest that they should be concerned about every infection. Instead, they reinforce the importance of routine prenatal care, recommended screening, vaccination before pregnancy when appropriate, safe food practices and discussing possible infections with healthcare professionals. The study also raises questions about whether children known to have experienced congenital infections should receive additional developmental monitoring as they grow. Early identification of developmental difficulties can allow children and families to access educational, behavioural and other supports when needed. Researchers say understanding which children face increased risks could ultimately help doctors provide more targeted follow-up. Autism itself is a complex neurodevelopmental condition. Scientists believe that many genetic and environmental factors can contribute to its development, and there is no single cause that explains all cases. The researchers therefore caution against interpreting the findings as evidence that autism can be explained by one particular pregnancy-related factor. The Swedish study adds another piece to the growing body of research into prenatal influences on brain development. Its large population size and long period of follow-up provide researchers with an opportunity to examine outcomes that may not become apparent until many years after birth.
Further research will be needed to determine whether particular infections, the timing of infection during pregnancy, the severity of infection or the body’s immune response are most important in determining developmental outcomes. Researchers also say future studies could help clarify the biological mechanisms involved and determine whether improved prevention or treatment of congenital infections could reduce some of the associated developmental risks. Overall, the findings point to an association between certain rare congenital infections and increased risks of autism and intellectual disability, while emphasizing that these infections represent only a small fraction of autism cases. For families, the research reinforces the importance of appropriate prenatal care and early developmental support rather than suggesting that infection exposure during pregnancy inevitably leads to autism or other developmental conditions.