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.

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.