LAUSR

Importance Neurodevelopmental disorders are associated with poor health and social outcomes. Population-based data on incidence, age at diagnosis, and demographic variations are essential to identify modifiable risk factors and inform the planning of services and interventions. Objectives To assess the incidence and timing of diagnosis of neurodevelopmental disorders during childhood in the US and to evaluate differences by population characteristics. Design, Setting, and Participants This population-based cohort study used nationwide data on birth cohorts nested in the 2000-2014 Medicaid Analytic eXtract and the 2003-2015 IBM MarketScan Research Database on 2 070 541 publicly and 1 309 900 privately insured children enrolled at birth. Data were analyzed between May 1, 2020, and June 30, 2021. Main Outcomes and Measures Neurodevelopmental disorders, autism spectrum disorders, attention-deficit/hyperactivity disorder, learning disabilities, speech or language disorders, developmental coordination disorders, intellectual disabilities, and behavioral disorders were identified based on validated algorithms. Kaplan-Meier analyses were used to estimate the incidence and timing of diagnosis, stratified by child's sex, birth year, maternal age at delivery, and race and ethnicity. Results The cohorts comprised 2 070 541 publicly insured children (1 045 426 boys [50.5%]) and 1 309 900 privately insured children (667 607 boys [51.0%]) enrolled at birth. By 8 years of age, 23.9% of publicly insured children and 11.0% of privately insured children received a diagnosis of 1 or more neurodevelopmental disorders (autism spectrum disorder, 1.6% and 1.3%; attention-deficit/hyperactivity disorder, 14.5% and 5.8%; learning disability, 1.2% and 0.6%; speech or language disorder, 8.4% and 4.5%; developmental coordination disorder, 0.9% and 0.7%; intellectual disability, 0.7% and 0.1%; and behavioral disorder, 8.4% and 1.5%). Risks were substantially higher among boys (incidence of ≥1 neurodevelopmental disorder by age 8 years for boys vs girls: 30.7% vs 16.7% among publicly insured children and 15.0% vs 6.7% among privately insured children) and White children (30.2% vs 9.1% among Asian children, 23.0% among Black children, 15.4% among Hispanic children, and 22.7% among children of unknown race or ethnicity; information on race and ethnicity was available only for publicly insured children). The association of maternal age and birth year with incidence of neurodevelopmental disorders varied by outcome. Except for attention-deficit/hyperactivity disorder, the diagnosis tended to be established somewhat earlier for privately insured children. The association of race and ethnicity with age at diagnosis varied by outcome. Co-occurring neurodevelopmental disorders were common, especially among children with autism spectrum disorder and intellectual disability (>70% had ≥1 other disorder). Conclusions and Relevance In this population-based cohort study, a relatively high incidence of and co-occurrence of neurodevelopmental disorders as well as the disparity in incidence and timing of diagnosis by insurance type and race and ethnicity were found. These findings represent important public health concerns and underscore the need for timely and accessible developmental assessments and educational services to help reduce the burden of these disorders.