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Maternal age increases risk of Autistic offspring

Posted Feb 09 2010 6:15am

Janie Shelton and colleagues at the University of Califonia at Davis reported that women over 40 years of age who give birth have an increased risk of the child having Autism. By studying a large sample of births, the researchers were able to disentangle the relative contributions of maternal and paternal age to the likelihood of having a child with Autism.

This study conflicts with some previous research that pointed at paternal age as a factor in Autism (see the EBD Blog page by Leslie Feldman on Fathers’ Age as Contributor to Risk for Autism ). The Shelton et al. analysis expressly examined the relative contributions and points at maternal age as an independent factor. Additional research will help to clarify the relationships.

Reports on autism and parental age have yielded conflicting results on whether mothers, fathers, or both, contribute to increased risk. We analyzed restricted strata of parental age in a 10-year California birth cohort to determine the independent or dependent effect from each parent. Autism cases from California Department of Developmental Services records were linked to State birth files (1990-1999). Only singleton births with complete data on parental age and education were included (n=4,947,935, cases=12,159). In multivariate logistic regression models, advancing maternal age increased risk for autism monotonically regardless of the paternal age. Compared with mothers 25-29 years of age, the adjusted odds ratio (aOR) for mothers 40+ years was 1.51 (95% CI: 1.35-1.70), or compared with mothers <25 years of age, aOR=1.77 (95% CI, 1.56-2.00). In contrast, autism risk was associated with advancing paternal age primarily among mothers <30: aOR=1.59 (95% CI, 1.37-1.85) comparing fathers 40+ vs. 25-29 years of age. However, among mothers >30, the aOR was 1.13 (95% CI, 1.01-1.27) for fathers 40+ vs. 25-29 years of age, almost identical to the aOR for fathers <25 years. Based on the first examination of heterogeneity in parental age effects, it appears that women’s risk for delivering a child who develops autism increases throughout their reproductive years whereas father’s age confers increased risk for autism when mothers are <30, but has little effect when mothers are past age 30. We also calculated that the recent trend towards delayed childbearing contributed approximately a 4.6% increase in autism diagnoses in California over the decade.

Writing for the Los Angeles (CA, US) Times, Thomas Maugh also covered this research. Mr. Maugh quotes one of the authors, Dr. Irva Hertz-Picciotto of the M.I.N.D. Institute (see left rail for a link): “There is a long history of blaming parents…. We’re not saying this is the fault of mothers or fathers. We’re just saying this is a correlation that will direct research in the future.” Read Mr. Maugh’s full story, “ Study links mother’s age to child’s risk of autism .”

Shelton, J. F. Tancredi, D. J., & Hertz-Picciotto, I. (2010). Independent and dependent contributions of advanced maternal and paternal ages to autism risk . Autism Research. Advance online publication. doi: 10.1002/aur.116

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