A woman’s chance of having a child with autism increase substantially as she ages, but the risk may be less for older dads than previously suggested, a new study analyzing more than 5 million births found.

Mothers older than 40 were about 50 percent more likely to have a child with autism than those in their 20s; the risk for fathers older than 40 was 36 percent higher than for men in their 20s.

Even at that, the study suggests the risk of a woman over 40 having an autistic child was still less than 4 in 1,000, one expert noted.