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Autism Risk Rises With Mother's Age

The Older the Mother, the Higher Her Child's Autism Risk
WebMD Health News
Reviewed by Louise Chang, MD

Feb. 8, 2010 -- The older a mother is when she gives birth, the higher her child's risk of autism, new data show.

A smaller effect also is seen for the age of the father, but only when the child is born to a father over age 40 and a mother under age 30.

The new findings come from a comparison of reported autism cases in California to state singleton birth records from 1990 to 1999. Over that time, there were about 5 million births and more than 12,000 autism cases.

The results:

  • Women over age 40 are 77% more likely than women under age 25 to have a child with autism.
  • Women over age 40 are 51% more likely than women aged 25-29 to have a child with autism.
  • Women aged 35-39 are 31% more likely than women aged 25-29 to have a child with autism.
  • Women aged 30-34 are 12% more likely than women aged 25-29 to have a child with autism.
  • Women under age 25 are 14% less likely than women aged 25-29 to have a child with autism.
  • Men over age 40 are twice as likely as men under age 25-29 to have a child with autism, but only if the mother is under age 25.

It's tempting to think that the trend for women to delay childbirth is behind the continuing rise of autism. But that's not the case. This trend accounts for less than 5% of the autism increase in California over the decade 1990-1999, calculate study researchers Janie F. Shelton, Daniel J. Tancredi, PhD, and Irva Hertz-Picciotto, PhD.

So what's going on? That isn't clear. Older parents' genes can undergo changes caused by aging and by the environment.

"We need to understand biologically why this is happening," Shelton tells WebMD. "It would be premature to tell older moms not to have a child. It could be the risk is associated with an exposure, and avoiding the exposure would be more important than not having kids at age 40."

Exactly what is a woman's risk of having a child with autism? The figures from the study come from 1990 to 1999. Autism cases increased throughout that decade -- and throughout the next decade, too.

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