Parent-Reported Prevalence of Autism Spectrum Disorders in US-Born Children: An Assessment of Changes within Birth Cohorts from the 2003 to the 2007 National Survey of Children’s Health

The prevalence of autism spectrum disorders (ASD) from the 2007 National Survey of Children’s Health (NSCH) was twice the
2003 NSCH estimate for autism. From each NSCH, we selected children born in the US from 1990 to 2000. We estimated autism
prevalence within each 1-year birth cohort to hold genetic and non-genetic prenatal factors constant. Prevalence differences
across surveys thus reflect survey measurement changes and/or external identification effects. In 2003, parents were asked
whether their child was ever diagnosed with autism. In 2007, parents were asked whether their child was ever diagnosed with
an ASD and whether s/he currently had an ASD. For the 1997–2000 birth cohorts (children aged 3–6 years in 2003 and 7–10 years
in 2007), relative increases between 2003 autism estimates and 2007 ASD estimates were 200–600 %. For the 1990–1996 birth
cohorts (children aged 7–13 years in 2003) increases were lower; nonetheless, differences between 2003 estimates and 2007
“ever ASD” estimates were >100 % for 6 cohorts and differences between 2003 estimates and 2007 “current ASD” estimates were >80 %
for 3 cohorts. The magnitude of most birth cohort-specific differences suggests continuing diagnosis of children in the community
played a sizable role in the 2003–2007 ASD prevalence increase. While some increase was expected for 1997–2000 cohorts, because
some children have later diagnoses coinciding with school entry, increases were also observed for children ages ≥7 years in
2003. Given past ASD subtype studies, the 2003 “autism” question might have missed a modest amount (≤33 %) of ASDs other than
autistic disorder.