Changes in Age of First Diagnosis of Autism Spectrum Disorder in Children Born Between 1992 and 2000

Background:  The early diagnosis of Autism Spectrum Disorders (ASD) is critical in improving outcomes for individuals and families affected by the disorder by allowing for timely access to interventions and healthcare. However, early intervention cannot be initiated when ASD diagnosis is delayed.

Objectives:  The primary objective of this study is to investigate trends in age of first ASD diagnosis over time. The secondary objective is to identify socio-demographic factors that may influence changes in age of ASD diagnosis over time.

Methods: This study investigated age of first ASD diagnosis among children born between 1992 and 2000. Participants were identified with ASD via population-based surveillance at 8 years of age via the South Carolina Autism and Developmental Disabilities Monitoring Program (SC ADDM), an ASD surveillance program conducted in collaboration with the Centers for Disease Control and Prevention (CDC). This study used a consistent methodology across all study years, thus limiting the impact of evolving interpretations of diagnostic criteria on the age of ASD diagnosis.  The timing of community-based ASD diagnosis was confirmed through records-based documentation.

Results:  The average age of first ASD diagnosis in this cohort was 56.1 ± 21.0 months. Age of first ASD diagnosis did not change across the identified SC ADDM study years, even when stratified by gender or race. Fewer than 25% of children received diagnoses before the age of 3, and the proportion of children receiving very early diagnoses (i.e. under age 3) did not change over time. Gender, race, and maternal education did not predict the age of first ASD diagnosis; however, children with an intellectual disability (IQ ≤70) were diagnosed with an ASD at an earlier age compared to those with IQ >70. 

Conclusions:  Study findings suggest that further efforts are needed to reduce the age of first ASD diagnosis in SC so that more children may have access to the early intensive treatments shown to be most effective for this population. Although the age of first diagnosis did not decline for children born between 1992 and 2000, the age of first ASD diagnosis may decrease in later cohorts due to improving public awareness about ASD, and the increased availability of diagnostic instruments for very young children.