Background: Autism spectrum disorder (ASD) represents one of the most significant neurodevelopmental disorders in early childhood, where early diagnosis, particularly in children under five years of age, is crucial for effective interventions. Although global autism incidence has risen due to improved awareness, enhanced screening programs, and broader diagnostic criteria, epidemiological data from middle-income countries like Iran remain limited, especially for children under five. This study aimed to examine autism incidence trends among Iranian children under five from 1990 to 2021, stratified by sex and province.
Methods: This ecological study was conducted from October 2024 to March 2025, analyzing data extracted from the Global burden of disease (GBD) database (1990-2021). Age-specific incidence data for children under five were obtained by sex and province. Incidence rates per 100,000 population were calculated for gender and provincial comparisons. Joinpoint regression analysis assessed annual trends and identified significant inflection points. Heat maps illustrated geographical distributions, while trend graphs stratified by sex and province were generated using GraphPad Prism.
Results: The incidence rate of autism in children under five gradually increased from 1990 to 2005, followed by a sharp rise between 2005 and 2009, reaching its peak during this period. A subsequent decline was observed from 2009 to 2021. The male-to-female ratio remained consistently stable at approximately 3:1 throughout the study period and across all provinces. Notable provincial disparities were observed, with border provinces exhibiting greater fluctuations compared to central regions.
Conclusion: In contrast to the continuous global increase, autism incidence among Iranian children under five demonstrated an initial rise followed by a sustained decline after 2009. This trend may be attributed to declining birth rates, demographic shifts, evolving diagnostic criteria, improved prenatal care, and persistent challenges in early screening and case registration, alongside regional disparities in access to diagnostic services. These findings emphasize the need for enhanced early-screening programs, equitable resource distribution, and evidence-based child mental health policies in Iran.
