Birth prevalence of autism spectrum disorders in the San Francisco Bay area by demographic and ascertainment source characteristics.

Using standardized methods for multi-source surveillance, we calculated the prevalence of autism spectrum disorders (ASD) among children born in a racially diverse region in 1994 or 1996 as 4.7/1000 live births. Children with ASD before age 9 were identified through chart abstraction at health-related sources; three-quarters were being served by the state-wide Department of Developmental Services. In adjusted models, we found a male:female ratio of 6:1, a doubling of ASD prevalence among children of older mothers (40+), and lower prevalence with lower paternal education. Children of Black or Hispanic mothers had lower prevalence than those of White, non-Hispanic mothers, but these differences were attenuated after adjustment. Prevalence in children of Asian mothers was similar to Whites. Potential under-counting is discussed.