Early autism spectrum disorder diagnoses on the rise, especially among boys

Manning SE. Pediatrics. 2011;127:1043-1051.

The number of early autism spectrum disorder diagnoses in Massachusetts increased during a recent 4-year period, according to study results.

The current study examined trends in autism spectrum disorder diagnoses by age 36 months, which the researchers defined as early diagnoses. Characteristics linked to early diagnosis were assessed.

The study population was a cohort of 388,644 infants born in Massachusetts between 2001 and 2005. Eligible infants were enrolled in an early-intervention program and received autism-related services if they were aged younger than 36 months by Dec. 31, 2008.

The final analysis involved 3,013 infants who had been enrolled in early-intervention programs. This was an incidence of 77.5 per 10,000 study population births. The incidence rate of autism spectrum disorder increased from 56 per 10,000 births in 2001 to 93 per 10,000 in 2005.

Early diagnosis was observed least frequently in infants of mothers aged younger than 24 years. For mothers aged younger than 20 years, the OR was 0.64 (95% CI, 0.47-0.87), and for mothers aged 20 to 24 years, the OR was 0.83 (95% CI, 0.70-0.98). Mothers whose primary language was not English (OR=0.68; 95% CI, 0.56-0.81) or who were foreign-born (OR=0.82; 95% CI, 0.72-0.93) also were less likely to have infants diagnosed. Mothers with at least 4 years of college — compared with mothers who were high school graduates — also had fewer infants diagnosed with autism spectrum disorders (OR=0.85; 95% CI, 0.75-0.96).

The risk for early diagnosis was increased in infants of mothers aged older than 30 years. For women aged 30 to 34 years, the OR was 1.27 (95% CI, 1.13-1.42) and increased with age (35-39 years, OR=1.39 [95% CI, 1.21-1.59]; 40-44 years, OR=1.52 [95% CI, 1.23–1.88]; ≥45 years, OR=2.03 [95% CI, 1.11-3.69]).

Boys were 4.5 times more likely than girls to receive a diagnosis of early autism spectrum disorder (95% CI, 4.1-5.0). Also among boys, the rate of early diagnoses increased from 88 per 10,000 births in 2001 to 151 per 10,000 in 2005, an increase of more than 70%. The increase was only 39% among girls during the same time period.

“Early autism spectrum disorder diagnoses are increasing in Massachusetts, reflecting the national trend observed among older children,” the researchers wrote. “Linkage of early-intervention program data with population-based vital statistics is valuable for monitoring autism spectrum disorder trends and planning development.”

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