Putting in place a new piece of the autism puzzle, researchers from UC Davis M.I.N.D. Institute have found that mom's age matters when it comes to evaluating a baby's risk for developing autism. Published online February 8, 2010, in the journal Autism Research, the study compared maternal and paternal age records of all births in California from 1991 to 1999 (4.9 million births) with lists from the California Department of Developmental Services identifying children born during the study period who were later diagnosed with autism (12,159 autism cases).
Researchers discovered that the risk of having a child with autism increased by 18 percent—nearly one-fifth—for every 5-year increase in the mother's age, starting from age 25. A 40-year-old woman's risk of having a child diagnosed with autism was 50 percent greater than that of a woman between 25 and 29 years old.
And what about dads? Fathers older than 40 boosted autism risk, too, but only when mothers were younger than 30. "Although fathers' age can contribute risk, the risk is overwhelmed by maternal age,'' says UC Davis researcher Janie Shelton, the study's lead author.
For example, among births to mothers younger than 25, children fathered by a man older than 40 were twice as likely to develop autism as those whose father was between 25 and 29. But once women reached age 30, fathers' ages mattered much less.
Before parents press the panic button, it's important to note that increased risks are small and that the vast majority of babies born to older mothers do not develop autism, points out Maureen Durkin, a University of Wisconsin researcher who also has studied the influence of a parent's age on autism, in an interview with the Associated Press.
Still, according to the study's authors, older parents may be more likely to have autoimmune conditions, including diabetes; and both have accumulated more toxins over their lifetimes—potentially damaging risk factors for sperm and eggs.
"We still need to figure out what it is about older parents that puts their children at greater risk for autism and other adverse outcomes, so that we can begin to design interventions," says Irva Hertz-Picciotto, another researcher involved with the study.