Socioeconomic Factors and Clinical Characteristics Associated with Age at Autism Spectrum Disorder Diagnosis

Objective: Investigate factors influencing autism spectrum disorder (ASD) diagnosis in children under and over 36 months, and determine the average age for ASD diagnosis at Charoenkrung Pracharak Hospital, Bangkok, Thailand, after implementing ASD screening. Materials and Methods: A retrospective cross-sectional study of 252 children with ASD aged 1-15 years from 2014 to 2023, classified into ≤36 months (n=104) and >36 months (n=148) at diagnosis. Demographic, clinical data and child/family factors were analyzed using multivariate regression analysis. Results: Mean age at ASD diagnosis was 44.77 ± 19.91 months. Attending well-baby clinics (aOR 2.64, p=0.038), higher family income ≥ 814 US dollars per month (aOR 2.33, p=0.020), and higher parental education (aOR 3.43, p=0.011) were significantly associated with diagnosis before 36 months. Hyperactivity as the main complaint (aOR 0.07, p=0.001) and global developmental delay/intellectual disability (aOR 0.45, p=0.023) predicted later diagnosis. Child’s gender, being an only child, sibling order, and parental age had no significant impact. Conclusion: Over half of all ASD diagnoses occurred after age 3, with an average age around 44 months. Regular attendance in well-child clinics allowing ASD screening, and higher socioeconomic status and parental education facilitated earlier diagnosis. In contrast, concerns about hyperactivity and global developmental delay often lead to delayed ASD assessment. Enhancing awareness of ASD among families with limited resources can promote timely diagnosis and access to intervention.