Early diagnoses of autism spectrum disorder are increasing in Massachusetts, particularly among boys, a study of 3,013 children who were enrolled in an early-intervention program has shown.
The study, published online May 16 in Pediatrics, linked data from state birth certificates and early-intervention program records. It showed that the incidence of autism spectrum disorders (ASDs) for children by age 3 increased 66% between 2001 and 2005, from 56 per 10,000, or 1 in 178, to 93 per 10,000, or 1 in 106. Early diagnoses increased among boys by more than 70%, from 88 per 10,000 children in 2001 to 151 per 10,000 in 2005. Diagnoses among girls, by contrast, increased 39% (doi: 10.1542/peds.2010-2943).
The findings, the investigators said, are broadly in keeping with national estimates published by the Centers for Disease Control and Prevention, which says an average of 1 in 110 U.S. children aged 8 years has Asperger’s disorder, autistic disorder, or pervasive developmental disorder, which all fall under the autism spectrum disorders.
For their research, Dr. Susan E. Manning and her colleagues matched data from a state ASD early-intervention program enrolling 3,013 children between 2001 and 2005 with birth certificate records, establishing successful links in 87.3% of cases.
Among the study’s additional findings was that ASD diagnoses were less common among infants of mothers 24 years old or younger and mothers whose first language was not English or who were foreign-born, reported Dr. Manning of the Massachusetts Department of Public Health, Boston, and the Centers for Disease Control and Prevention, Atlanta, and her colleagues, Odds of diagnosis were 4.5 (95% confidence interval, 4.1-5.0) times higher for boys than girls. Maternal age over 30 was associated with an elevated risk of diagnosis. Differences in rates of diagnosis among ethnic groups were narrower in 2005 than in 2001, the investigators found, and birth weight was the only variable seen differing significantly between boys and girls with ASDs (15.7% of girls had low birth weight, compared with 11% of boys), the investigators said (Pediatrics 2011;127:1043-51).
Symptoms of ASDs, particularly autism disorder, can be evident before 3 years, and "[m]ounting evidence suggests that early initiation of intensive intervention can improve developmental outcomes for children with ASDs," Dr. Manning and her colleagues wrote. Massachusetts established its early-intervention program in 1998 to provide specialty services to children with ASDs with the aim of improving outcomes. Altogether, 1 in every 129 Massachusetts children born between 2001 and 2005 was enrolled in early intervention with an ASD by the age of 36 months.
Among the limitations of the study is that confirmation of ASDs was not available for all children. "Thus our case definition might be overly inclusive," they wrote. "It is possible that ASDs might have been initially suspected because of the positive initial screen but subsequently ruled out. These factors would lead to an overestimation of early diagnosis of ASDs."
On the other hand, the findings might underestimate early diagnoses, the authors wrote, because some children who are on the spectrum might not participate in early-intervention programs, and would therefore be missed by the study. Nevertheless, the data are useful.
"Our analysis shows that linkage of early-intervention program data and population-based vital statistics data is useful for identifying trends and disparities in early ASD diagnoses," they wrote. "The results of this type of analysis can be used to increase clinician awareness of the early signs of ASDs and inform state early-intervention program efforts to anticipate future service demands and resources needed."
The study was financed by the Massachusetts Department of Public Health. None of its authors declared financial conflicts of interest except Karen Clements, Sc.D., who disclosed employment with i3 Innovus, a subsidiary of United Health Group that has a financial interest in the early diagnosis of autism.