Impact of birth weight on long-term growth and development in children: evidence from a nationwide cohort study

Birth weight (BW) is a well-established key marker of early health, but its long-term influence on growth and development in the general pediatric population remains uncertain. This study aimed to assess the longitudinal association of BW on growth and neurodevelopment from infancy to six years of age using nationwide population-based data from Korea. We analyzed data from 3,033,843 children born between 2013 and 2020 who participated in the Korean National Health Insurance Service infant and child health screening program. Participants were stratified into five birth weight categories (< 1,000; 1,000–1,499; 1,500–2,499; 2,500–3,999; and ≥ 4,000 g) and followed across seven screening rounds. Growth and neurodevelopmental outcomes were assessed using standardized anthropometric measures and the Korean Developmental Screening Test for Infants and Children (K-DST), respectively. Longitudinal patterns were examined at each round, and the primary analysis focused on outcomes at 30–36 months using multivariable logistic regression to identify risks for growth failure and screening-positive developmental delay. Across screening rounds, children with lower BWs, especially those under 1,500 g, showed consistently lower growth percentiles and higher rates of K-DST screen-positive results. At 30–36 months, infants with BW < 1,000 g had substantially higher odds of growth failure across all three anthropometric measures (height, weight, and head circumference) (aOR range 25.2–43.1 vs. ≥ 2,500 g; all p < 0.001) and of screening positive for developmental delay (K-DST < − 2 SD) (aOR 3.62, 95% CI 3.12–4.21, p < 0.001). Male sex and neonatal morbidities such as bronchopulmonary dysplasia, periventricular leukomalacia, and hypoxic-ischemic encephalopathy were also associated with growth failure and developmental delay at 30–36 months. Disparities in growth and development persisted across screening rounds, particularly among the < 1,500 g BW groups. Lower BW, particularly < 1,500 g, was associated with higher odds of growth failure and screening-positive developmental risk at 30–36 months, with disparities in growth and development persisting through early childhood.