While there has been an increase in the number of children with autism spectrum disorder (ASD) undergoing their first evaluation in the preschool years, a new study shows that the population rates of ASD still remain much higher in eight-year-olds than in four-year-olds. The findings suggest that many ASD cases aren’t being recognized until after school age, especially in cases without obvious intellectual impairment.
The research is published in the Journal of Developmental & Behavioral Pediatrics.
For the study, the researchers analyzed 2010 data from five of eleven US sites participating in the Centers for Disease Control and Prevention’s Autism and Developmental Disabilities Monitoring (ADDM) Network. The prevalence of ASD was assessed by screening and review of the children’s health and/or education records.
Population rates of ASD among four-year-olds (born in 2006) were compared with those in eight-year-olds (born in 2002) in the same areas.
In the overall population of nearly 58,500 four-year-olds, the estimated prevalence of ASD was 13.4 per 1,000 children. These figures varied widely across sites: from 8.5 per 1,000 in Missouri to 19.7 per 1,000 in New Jersey.
The findings show that estimates of ASD prevalence were about 30 percent lower in four-year-olds compared to eight-year-olds, suggesting that many cases aren’t being recognized until after school age — especially in ASD children without cognitive (intellectual) impairment.
Eight-year-old children had a 40 percent higher prevalence of ASD without cognitive impairment compared to four-year-old children. The reverse was true for ASD plus cognitive impairment: four-year-olds had a 20 percent higher prevalence compared to eight-year-olds.
In a promising trend, more children with autism underwent their first comprehensive evaluation at a younger age. In children diagnosed with autism by age four, the median age at initial evaluation was 27 months for children born in 2006 versus 32 months for those born in 2002.
Increasing the percentage of children with ASD who receive a comprehensive evaluation before 36 months is a major part of efforts to improve recognition and treatment of these disorders.
There was some evidence of racial/ethnic differences as well. Among four-year-olds, rates of early evaluation were lower in black children than in white children. However, this discrepancy was smaller among children with ASD plus cognitive impairment. Boys were less likely to have early evaluation than girls.
Estimates of ASD prevalence were consistently higher at sites where both education and health records were available. This highlights the valuable role of the special education system in identifying preschoolers with developmental disorders.
“While ASD is considered a lifelong condition, evidence suggests that early intervention can improve outcomes,” writes Dr. Daisy Christensen of the National Center on Birth Defects and Developmental Disabilities and colleagues.
Early identification and access to special services can improve outcomes for children with ASD. The new findings suggest progress toward that goal, with more children with ASD receiving recommended comprehensive evaluation by age 36 months. But estimates of ASD prevalence remain consistently lower in four-year-olds compared to eight-year-olds, suggesting that more cases will be recognized as the children reach school age.
“Continued efforts should be made to promote early identification of children with ASD so that interventions can be initiated at the youngest age possible,” say the researchers. They plan further follow-up to keep track of the trends in ASD prevalence.
Source: Wolters Kluwer Health