Sibling Influence on Childhood Neurodevelopmental Disorders: A Cohort Study in Taiwan

Purpose Autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), and cerebral palsy (CP) are neurodevelopmental disorders that impose lasting burdens on families. Birth order and sibling presence may influence neurodevelopmental risks, providing critical insights for early intervention and public health policies. Method This study analyzed 2,045,178 children from Taiwan’s Birth Registration Database (2004–2014), linked to National Health and Death Registries through 2020. Children were categorized by sibling status (single child, first-born, second-born, third-or-later-born) to examine birth order effects on CP, developmental delay, ASD, and ADHD. Kaplan-Meier and Cox proportional hazards models were used, accounting for birth outcomes, socioeconomic status, and urbanization. Results Children with siblings had lower neurodevelopmental disorder risks than single children. ASD and ADHD risks declined with increasing birth order, while first-born siblings had higher risks of ADHD and developmental delay compared to later-born children. Subgroup analyses consistently showed that sibling presence was associated with reduced risks. Conclusion Birth order and sibling presence influence neurodevelopmental disorder risks, with single children at higher risk. These findings are particularly relevant given declining birth rates in developed countries and highlight the need for targeted screening and intervention strategies for high-risk groups.