We examined trends in autism spectrum disorder diagnoses by age 36 months (early diagnoses) and identified characteristics associated with early diagnoses.
Massachusetts birth certificate and early-intervention program data were linked to identify infants born between 2001 and 2005 who were enrolled in early intervention and receiving autism-related services before age 36 months (through December 31, 2008). Trends in early autism spectrum disorders were examined using Cochran-Armitage trend tests. χ2 Statistics were used to compare distributions of selected characteristics for children with and without autism spectrum disorders. Multivariate logistic regression analyses were conducted to identify independent predictors of early diagnoses.
A total of 3013 children (77.5 per 10 000 study population births) were enrolled in early intervention for autism spectrum disorder by age 36 months. Autism spectrum disorder incidence increased from 56 per 10 000 infants among the 2001 birth cohort to 93 per 10 000 infants in 2005. Infants of mothers younger than 24 years of age, whose primary language was not English or who were foreign-born had lower odds of an early autism spectrum disorder diagnosis. Maternal age older than 30 years was associated with increased odds of an early autism spectrum disorder diagnosis. Odds of early autism spectrum disorders were 4.5 (95% confidence interval: 4.1–5.0) times higher for boys than girls.
Early autism spectrum disorder diagnoses are increasing in Massachusetts, reflecting the national trend observed among older children. Linkage of early-intervention program data with population-based vital statistics is valuable for monitoring autism spectrum disorder trends and planning developmental and educational service needs.