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Importance: Despite the increasing prevalence of autism spectrum disorder (ASD) in the US, underlying temporal trends in newly recorded diagnoses remain poorly understood. Objective: To evaluate age- and sex-specific incidence trends of ASD from 2016 to 2024 and quantify the temporal patterns before and after the COVID-19 pandemic and diagnostic substitution. Design, Setting, and Participants: This retrospective cohort study used electronic health record data from a large US health care system. Analyses were conducted from October to December, 2025. The study population included 171 134 participants (stratified as children 0-9 years, adolescents 10-18 years, and adults ≥19 years) who maintained continuous engagement with the health care system, defined as having at least 1 clinical encounter annually from 2016 to 2024. Main Outcomes and Measures: The primary outcome was the annual incidence of newly recorded diagnoses of International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10) codes F84.0 and F84.5. Temporal trends were analyzed using joinpoint regression to calculate annual percentage changes (APCs) and identify significant inflection points. Results: Among 171 134 participants (mean SD age, 26.78 16.38, 63.8% female), females received autism diagnoses a mean (SD) of 3.4 years later than males (age at diagnosis, 15.7 years for female individuals vs 12.3 years for male individuals; P < .001). Male autism incidence remained stable or declined 2016 to 2024; female incidence increased significantly post-2020 (APC, 19.0%; 95% CI, 12.1% to 33.4%). In the pediatric cohort, decreasing annual incidence among males (APC, -2.0%; 95% CI, -3.7% to -0.3%; to APC, -2.0%, 95% CI, -3.7% to -0.3%) alongside increasing incidence for females since 2020 (APC, 17.4; 95% CI, 9.0% to 45.3%). In adolescent males, incidence declined from 2016 to 2018 (APC, -29.6%; 95% CI, -48.9% to -1.2%), and stabilized from 2018 to 2024. In adolescent females, autism incidence increased significantly between 2020 and 2024 (APC, 22.3%; 95% CI, 6.1% to 62.8%). In adult males, autism incidence showed a downward trend in the 2016 to 2024 period, while in adult females, the APC from 2016 to 2024 was positive, but the finding was not statistically significant (APC, 8.0%; 95% CI, -0.9% to 20.0%). Conclusions and Relevance: In this cohort study, ASD diagnoses increased disproportionately among females after 2020 while remaining stable or declining among males. These patterns suggested that increasing ASD prevalence reflected improved identification of historically underrecognized presentations rather than a uniform population-level increase. These findings highlight the need for screening strategies that address sex-specific presentations.
Messias et al. (Wed,) studied this question.