Characterizing the Prevalence of Co‐Occurring Neurodevelopmental Conditions and Associations With the Timing of Diagnosis in Autism in Medicaid Claims Data

ABSTRACT Autism commonly co‐occurs with other neurodevelopmental conditions (NDCs), although diagnostic trajectories of an autism diagnosis relative to other NDCs are not well understood. We sought to examine the prevalence of NDCs within autistic children and how co‐occurrence is associated with the timing of autism diagnoses. All children born between January 1, 2014 and December 31, 2015, and who had continuous enrollment in North Carolina Medicaid between less than 1 month old through autism diagnosis were included. This time period was chosen because follow‐up data is available through December 31, 2022, which allowed inclusion of children to at least 8 years of age. From a cohort of 91,907 children, we identified 2694 children (77% boys) diagnosed with autism spectrum disorder. We found language (82%) and global developmental (52%) delays the most prevalent co‐occurring NDCs. Within the most common combinations of co‐occurring NDCs, over half (55%) of autistic children were diagnosed with three combinations of NDCs (24% with motor, language, and global developmental delays; 16% with language delay only; 16% with language and global developmental delays). Diagnoses of NDCs are associated with earlier autism diagnoses, with autism diagnoses occurring 10.8 months earlier for developmental, 8.4 months for language, and 7.2 months earlier for motor delays than children without these co‐occurring diagnoses. Earlier autism diagnoses were especially evident in children who received neurodevelopmental delay diagnoses between 1.5 and 2 years of age. These findings are clinically relevant for developmental screening in children with neurodevelopmental disorders and intervention recommendations for autistic children.