The prevalence of autism spectrum disorder (ASD) has risen throughout the last 20 years, but why? Increasing rates of ASD diagnosis have occurred alongside an increase in parental age. Some studies have suggested that older mothers and fathers are more likely to have children with ASD. A new study finds that there is an increased risk of having a child with ASD for older parents, but that risk is small—only 2.7 percent overall. The researchers suggest instead that awareness of the disorder and changes to diagnostic procedures can account for increased autism prevalence.
The researchers analyzed birth information for 927,003 children born in New York City from 1994 to 2001. The cohort included 1,640 children with ASD. The data came from the Longitudinal Study of Early Development, which gathers health and education statistics on children born to women in New York. For the analysis, the researchers grouped the parents by age into four categories: under 25, 25 to 29, 30 to 35, and over 35.
During the study period, the proportion of children born to a mother over age 35 increased by 15 percent and children born to a father over age 35 increased by 10 percent. The prevalence of ASD increased from 1 in 3,300 to 1 in 233 over the same period. Compared to mothers under age 25:
- Mothers aged 25 to 29 were 1.5 times more likely to have a child with ASD.
- Mothers aged 30 to 34 were 1.6 times more likely to have a child with ASD.
- Mothers over age 35 were 1.9 times more likely to have a child with ASD.
Men over age 35 were 1.4 times more likely to have a child with ASD than men under age 25, which corroborates the findings from a Danish study published in 2012.
The results show that parental age—maternal and paternal—is a relatively small risk factor for ASD. It is not known why parental age affects the risk of ASD.
This research is published in Maternal and Child Health Journal.
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