Scientists Just Debunked a Major Myth About Autism

For years, studies have suggested that a mother’s health during pregnancy could influence her child’s likelihood of developing autism. However, a groundbreaking new study, leveraging Denmark’s extensive medical records, reveals a different story.

Researchers found that nearly all previously suspected maternal conditions were not actually causing autism but were instead linked through genetics or environmental factors. The only consistent associations with autism came from fetal complications, which scientists now believe are early signs of autism rather than its cause.

Rethinking Autism Risk Factors

Many studies have suggested a link between a mother’s health during pregnancy and her child’s risk of autism. However, a new study finds that nearly all of these connections can be explained by other factors, such as genetics, environmental exposures like pollution, and access to healthcare.

Conducted by researchers at NYU Langone Health, the study found that the only pregnancy-related conditions truly associated with autism were complications affecting the fetus. This suggests that these complications may not be causes of autism but rather early signs of it.

No Evidence That Maternal Health Causes Autism

“Our study shows that there is no convincing evidence that any of these other diagnoses in the mother can cause autism,” said study senior author Magdalena Janecka, PhD, an associate professor in the Department of Child and Adolescent Psychiatry and in the Department of Population Health, at NYU Grossman School of Medicine.

Publishing in the journal Nature Medicine online Jan. 31, the new study included an analysis of
the medical histories of more than 1.1 million pregnancies (among 600,000 mothers) from a national registry in Denmark. Unlike medical records in the United States, which are often scattered among many different medical providers an individual sees during their lifetime, in Denmark all of an individual’s health records are consolidated under a single government-issued number, which enabled researchers to check each woman for more than 1,700 distinct diagnoses as defined by international standards, known as ICD-10 codes. From these, researchers focused their analysis on those diagnosed in at least 0.1% of pregnancies (236 diagnoses).

“We believe our study is the first to comprehensively examine the entire medical history of the mother and explore a wide range of possible associations, controlling for multiple concurrent conditions and confounding factors,” said study lead author Vahe Khachadourian, MD, PhD, MPH, a research assistant professor in the Department of Child and Adolescent Psychiatry at NYU Grossman School of Medicine.

Denmark has strict safeguards in place to prevent misuse of the registry data, says Janecka, since it contains personal information. However, because of the individual-specific information, the researchers were able to cross-check every diagnosis a woman had had with her children’s risk of autism.

Untangling the Genetic and Environmental Puzzle

For the study, the researchers corrected for factors that could confound, or offer an alternative explanation for, the link between the diagnosis a woman received and a child’s autism diagnosis. These factors include sociodemographic status and the mother’s age during pregnancy, since children of older mothers are more likely to be diagnosed with autism, and their mothers are also more likely to receive certain diagnoses, such as hypertension, than their younger counterparts.

After accounting for these confounding factors, as well as for concurrent diagnoses, 30 were still statistically associated with autism in the child. To determine if these happened to occur alongside rather than cause autism, the researchers then included the siblings of autistic children in the analysis. If a mother was diagnosed with the same condition during pregnancies of children with and without autism, then it would suggest that factors other than her diagnosis were influencing the link with autism. This step disentangled the conditions that could be attributable to familial factors, such as genetics and environmental exposure to pollution, from those that may be causing autism.

The Role of Genetics in Autism Risk

According to the researchers, genetics is a strong familial confounder (plausible explanation) for autism. Some of the same genes linked to depression are also associated with autism. If a mother experiences depression during pregnancy and her child is later diagnosed with autism, it is more likely due to shared genetic factors rather than depression itself affecting the fetus during development.

Researchers also analyzed fathers’ medical histories. Any association between a paternal diagnosis and autism would most likely be caused by familial factors, since the father’s direct effects on a fetus postconception are likely very limited. In fact, the researchers observed that a lot of paternal diagnoses are just as related to child autism as the maternal diagnoses.

Fetal Complications: Early Signs, Not Causes

After accounting for the familial factors, the only maternal diagnosis that was still strongly statistically associated with autism was pregnancy complications related to the fetus.

“Our interpretation is that these fetal diagnoses likely do not cause autism, but are instead early signs of it,” said Janecka. “The predominant hypothesis is that autism really starts prenatally. Even before a child receives a diagnosis for autism, developmental changes have been happening the entire time.

Shifting the Narrative for Parents

“Many mothers of children with autism feel guilty about it,” said Janecka, “thinking that they did something wrong during pregnancy, and it is heartbreaking. I think showing that these things are not going to cause autism is important and may lead to more effective ways to support autistic children and their families.”

Autism is a developmental disorder that typically emerges in childhood, affecting social interactions and behavior. Symptoms can vary widely and may include reduced eye contact, difficulty engaging in play, repetitive movements or speech, and unusual responses to sensory experiences like temperature. While these traits can persist into adulthood, they differ from person to person. According to federal estimates, autism affects about 1 in 54 children in the United States.

Reference: “Familial confounding in the associations between maternal health and autism” by Vahe Khachadourian, Elias Speleman Arildskov, Jakob Grove, Paul F. O’Reilly, Joseph D. Buxbaum, Abraham Reichenberg, Sven Sandin, Lisa A. Croen, Diana Schendel, Stefan Nygaard Hansen and Magdalena Janecka, 31 January 2025, Nature Medicine.
DOI: 10.1038/s41591-024-03479-5

Funding support for the study was provided by National Institutes of Health grants R01MH124817 and T32MH122394, Lundbeck Foundation grants R102-A9118 and R155- 2014-1724, the Seaver Foundation, and the Eunice Kennedy Shriver National Institute of Child Health and Human Development grant HD098883.

Other study co-investigators are Elias Speleman Arildskov, Jakob Grove, and Stefan Nygaard Hansen at Aarhus University in Denmark; Paul O’Reilly, Joseph Buxbaum, Abraham Reichenberg, and Sven Sandin at Icahn School of Medicine at Mount Sinai in New York City; Lisa Croen at Kaiser Permanente Northern California in Oakland; and Diana Schendel at Drexel University in Philadelphia.

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