Many investigations have pointed towards a connection between a mother’s health issues during pregnancy and the likelihood of her child developing autism. However, new research indicates that most of these “links” can be attributed to other factors, such as genetics, environmental pollution, and healthcare access.
The study, conducted by NYU Langone Health researchers, found that the few health conditions genuinely linked to autism were mostly complications related to the fetus. This led the authors to suggest that these symptoms might actually indicate early signs of autism in the child rather than being a cause of it.
“Our research indicates that there is no strong evidence that any other diagnoses in the mother contribute to autism,” stated the study’s senior author, Magdalena Janecka, PhD, associate professor in the Department of Child and Adolescent Psychiatry and the Department of Population Health at NYU Grossman School of Medicine.
Published online on January 31 in the journal Nature Medicine, the new research analyzed the medical histories of over 1.1 million pregnancies (involving around 600,000 mothers) from a national registry in Denmark. Unlike in the United States, where medical records can be fragmented among various providers, Denmark keeps all health records under one government-issued number, allowing researchers to review more than 1,700 distinct diagnoses by using the international standards known as ICD-10 codes. Their focus narrowed down to those conditions diagnosed in at least 0.1% of pregnancies, totaling 236 diagnoses.
“We believe our study is the first to thoroughly investigate the comprehensive medical history of mothers and evaluate a broad range of potential associations, while accounting for multiple coexisting conditions and confounding factors,” said Vahe Khachadourian, MD, PhD, MPH, the lead author and a research assistant professor in the Department of Child and Adolescent Psychiatry at NYU Grossman School of Medicine.
Janecka explained that Denmark’s stringent protections against misuse of registry data, which includes sensitive personal information, allowed researchers to cross-check each diagnosed condition a woman had with her children’s risk of autism.
In this study, the researchers adjusted for various confounding factors that could provide alternative explanations for the established link between a woman’s diagnosis and her child’s possible autism diagnosis. These included socio-demographic details and the mother’s age during pregnancy, considering that older mothers tend to have higher rates of autism diagnoses in their children and are also more likely to be diagnosed with specific conditions, such as hypertension.
After controlling for these confounding factors, as well as concurrent diagnoses, 30 conditions were still statistically correlated with autism in children. To investigate whether the conditions occurred simultaneously or played a causal role, the researchers included siblings of autistic children in their analysis. If a mother was diagnosed with the same condition during pregnancies of both autistic and non-autistic children, it would suggest that factors unrelated to her diagnosis influence the risk of autism. This step helped differentiate between conditions stemming from family traits, like genetics and exposure to pollution, and those that may be responsible for causing autism.
The researchers noted that genetics plays a significant role in autism risk. Certain genes associated with an increased likelihood of depression are also linked to autism. Thus, if a woman experiences depression while pregnant and her child is diagnosed with autism, it is much more likely that both mother and child share genetic factors that contribute to both conditions, rather than the depression chemically affecting the fetus to cause autism.
The team also reviewed the medical histories of fathers. Any correlation between a father’s diagnosis and autism would likely stem from familial factors, as a father’s direct impact on a fetus after conception is generally limited. The researchers found that many paternal diagnoses were just as closely linked to child autism as maternal diagnoses.
After accounting for these family-related factors, the only maternal diagnosis that remained strongly associated with autism was complications during pregnancy related to the fetus.
“We interpret this to mean that these fetal diagnoses are likely not causal for autism but are instead early indicators of it,” Janecka explained. “The prevailing hypothesis is that autism begins during the prenatal period, as developmental changes are occurring even before a formal autism diagnosis is made.”
Janecka also noted, “Many mothers of children with autism feel guilty, believing they did something wrong during pregnancy, which is heartbreaking. It’s crucial to demonstrate that these factors do not cause autism, potentially leading to better support strategies for autistic children and their families.”
Autism is recognized as a developmental disorder prevalent in childhood, characterized by various challenges in social interaction and repetitive behaviors. Symptoms can vary significantly into adulthood and may include limited eye contact, reluctance in play interactions, repetitive movements or sounds, and lack of sensitivity to temperature changes. Federal estimates suggest that approximately one in every 54 children in the United States is affected by autism.
The study received funding from several sources, including National Institutes of Health grants R01MH124817 and T32MH122394, Lundbeck Foundation grants R102-A9118 and R155-2014-1724, the Seaver Foundation, and Eunice Kennedy Shriver National Institute of Child Health and Human Development grant HD098883.
Additional co-investigators in the study included Elias Speleman Arildskov, Jakob Grove, and Stefan Nygaard Hansen from Aarhus University in Denmark; Paul O’Reilly, Joseph Buxbaum, Abraham Reichenberg, and Sven Sandin from Icahn School of Medicine at Mount Sinai in New York City; Lisa Croen from Kaiser Permanente Northern California in Oakland; and Diana Schendel from Drexel University in Philadelphia.
