Birth Order Difference in Neurodevelopment Appears Within the First Year of Life
Summary
Using Ages & Stages Questionnaires?, Third Edition (ASQ?-3), researchers found birth order differences in neurodevelopment within first year of life
Birth order, a non-genetic factor, may influence early neurodevelopment. A nationwide Japanese birth cohort study based on sibling pairs suggests that differences in neurodevelopment emerge during the first year of life. Second-born infants scored slightly lower than firstborns across several domains and had lower levels of parental engagement. The study suggests that differences in caregiver-reported parental engagement may partly account for these small but consistent early developmental gaps, though their long-term clinical significance remains unclear.
- Image title： Birth Order Differences in Neurodevelopment Emerge Within the First Year
- Image caption： A large Japanese cohort study used a within-family design to compare early neurodevelopmental outcomes among pairs of firstborn and second-born singleton children enrolled in the Japan Environment and Children’s Study (JECS). The findings suggest that small but consistent birth order differences in neurodevelopment are observable within the first year of life. Differences in parental engagement were also observed between siblings.
- Credit： Dr. Akiko Tsuchida from the University of Toyama, Japan
- License type： Original content
- Usage restrictions： Credit must be given to the creator.
Research Details
Birth Order Difference in Neurodevelopment Appears Within the First Year of Life[PDF, 519KB]
Reference
Title of original paper
Birth Order Differences in First-Year Neurodevelopment
Journal
JAMA Network Open
DOI
https://doi.org/10.1001/jamanetworkopen.2026.1265
Additional information for EurekAlert
Latest Article Publication Date
06 March 2026
Method of Research
Data/statistical analysis
Subject of Research
People
Conflicts of Interest Statement
Dr Matsumura reported receiving research funding from the Japan Society for the Promotion of Science (JSPS KAKENHI) and an honorarium from Sumitomo Pharma for a contributed manuscript within the past 36 months, outside the submitted work. No other disclosures were reported.
Media contact
Yumiko Kato
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