Is Parental Age Related to Autism Risk?

William T. Basco, Jr., MD, FAAP


August 03, 2007

Maternal and Paternal Age and Risk of Autism Spectrum Disorders

Croen LA, Najjar DV, Fireman B, Grether JK
Arch Pediatr Adolesc Med. 2007;161:334-340


The authors note that previous studies had been inconsistent in their findings of whether maternal age was related to risk of autism and autism spectrum disorders (ASD) in offspring. This study sought to address some of the limitations of previous studies by including paternal data, data on birth order, as well as other potential confounding factors in assessing the relationship between maternal age and risk of ASD in offspring.

This study evaluated a cohort of over 134,000 children born to California Kaiser Permanente hospitals from 1995 to 1999. The clinic visits and diagnoses of the children were tracked through administrative records. Of the eligible children, 593 were diagnosed with ASDs (an ASD diagnosis must have appeared at least twice in outpatient administrative records).

Forty-seven percent of the children diagnosed with ASD were diagnosed with autism, with the remaining 53% having pervasive developmental disorder-not otherwise specified or Asperger's syndrome. The mean length of administrative data follow-up for all subjects was 67.5 months (> 5 years). Mean maternal age was 28.8 years, and mean paternal age was 31.5 years. There was a high correlation between maternal and paternal ages, so each was used in models without the other to evaluate risk.

The authors utilized age as both a continuous and categorical (by age grouping) variable in analyses. Both methods demonstrated increased risk of ASD with increasing age, so only the continuous numbers are summarized here. For all ASDs, 10-year increases in maternal age and paternal age were associated with 31% and 28% increases in relative risk of ASD in offspring, respectively, after controlling for birth order, gender, maternal education, paternal education, and race/ethnicity of the parents. The relative risk of having an ASD for males was more than 5 times (> 500%) that of female offspring.

Maternal education was associated with a 44% increased risk of ASD in children, even after controlling for maternal age. Paternal education and maternal and paternal race/ethnicity were not associated with ASD.

When the diagnoses were separated -- looking at just autism or pervasive developmental disorder-not otherwise specified + Asperger's syndrome -- the overall pattern of maternal and paternal age being associated with increased risk held, but several of the 95% confidence intervals for the relative risks included "1," making the associations not significant.

The authors conclude that older parental ages, for both mothers and fathers, is associated with higher risk of their offspring having an autism spectrum disorder.


While this study addresses many covariates of interest, the use of administrative data prevented the researchers from including sibling and extended family history of autism. Nevertheless, the findings are interesting and show that parental age is related to autism risk even after controlling for education, year of birth, and birth order. The fact that birth year was significant also suggests that there are significant temporal trends in autism diagnosis that we may not fully understand. The temporal trends may be related to increasing parental awareness, increasing provider familiarity with autism and ASD symptoms leading to better ascertainment, and likely a combination of all of these and other factors. Finally, the finding that higher maternal education is associated with increased risk, even after controlling for maternal age, is a fascinating finding and leads one to wonder what factors (increased maternal ascertainment or true biological mechanism) might be associated with educational achievement or ability and risk for autism in offspring.



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