Autism researchers study the link between parental age and autism risk because the relationship provides important clues to the factors that lead to autism. For example, increasing age may bring greater cumulative exposure to toxic chemicals. Older moms have increased risk of pregnancy complications, and as a woman’s eggs age, they are more likely to carry genetic changes that can affect fetal development.
Understanding these risk factors and associated biological pathways can guide further research into understanding, preventing and treating autism. However, experts agree that the increased risk associated with any of these influences is modest and likely involves a combination with other factors that increase risk.
But while multiple studies have confirmed that older fathers have a slightly increased risk of having a child affected by autism, studies on older moms have varied in their findings.
To gain a clearer picture, investigators with the International Collaboration for Autism Registry Epidemiology (iCARE) conducted a meta-analysis of all studies on maternal age and autism risk conducted over the past 20 years. Meta-analysis is a statistical approach for reanalyzing the results of multiple studies to gain a clearer picture of their combined results. This and other iCARE investigations into environmental risk factors are supported by research grants from Autism Speaks. (In this context, “environmental” refers to any influence beyond genetic predisposition, including parental age, birth complications, etc.)
After excluding studies lacking sufficient information for reliable analysis, the investigators selected 16 published research papers that included 25,687 cases of autism spectrum disorder (ASD) and over 8.6 million subjects without ASD.
They found that, on average, the risk of having a child with autism was approximately 50 percent higher for a 35-year-old mother than for a mother in her mid to late 20s. This increased risk, still relatively modest, remained even after the researchers considered such factors as the age of the father. By contrast, there was little difference in risk between 20-year-old moms and those ages 25 to 29. The report appears online in advance of its publication in the May issue of the Journal of the American Academy of Child and Adolescent Psychiatry.
The researchers note that the age of parenting has been increasing in the United States and Europe in recent decades, and an association between parental age and autism may be one factor behind autism’s increasing prevalence over the past two decades.
“It is important to realize that ‘risk’ is not the same as ‘cause,’” says Michael Rosanoff, M.P.H., Autism Speaks associate director for public health research and scientific review. “Although this study indicates that older mothers are at increased risk for having a child with autism, maternal age is likely only part of a bigger picture where, in combination with other factors, it can increase risk for autism.”
For more perspective on “Risk vs Cause,” please see our recent “Got Questions?” blog post by Martha Herbert, M.D., author of The Autism Revolution: Whole Body Strategies for Making Life All It Can Be. You can learn more about iCARE and its Autism Speaks-supported research here and here. These studies as well as a wealth of related research on autism risks, therapies and supportive services are made possible by the passionate support of Autism Speaks’ community of families, volunteers and donors. Learn more about these efforts and how you can help here.