BackgroundLow birth weight (LBW) is a significant global health concern with potential health risks and developmental implications for infants. Catch-up growth, an accelerated growth following an inhibition period, may partially compensate for growth deficits in LBW children. AimsThis study investigated the prevalence of LBW and catch-up growth in height, weight, and body mass index (BMI) among LBW children in Japan, identified factors associated with LBW, and explored the potential for catch-up growth at different ages up to seven years. Study design and subjectsThe Hokkaido birth cohort study included 20,926 pregnant Japanese women recruited during their first trimester from 37 hospitals and clinics. Follow-up assessments were conducted in children up to seven years of age, tracking LBW children's growth and development using the Maternal and Child Health Handbook, and providing valuable insights into catch-up growth patterns. Outcome measuresLBW was defined as a neonatal birth weight of <2500 g. The primary outcomes were catch-up growth in height, weight, and BMI at different ages. Z-scores were calculated to assess growth parameters with catch-up growth, defined as a change in z-score (> 0.67) between two time points. Results and conclusionsA LBW was prevalent in 7.6 % of the cohort, which was lower than that reported in other Japanese studies. Among LBW children, 19.3 % achieved catch-up growth in height by age seven, and 10.6 % in weight. Catch-up growth in LBW children could partially offset these deficits. Further research will help understand the long-term outcomes and inform interventions for healthy development.