Japanese growth charts stratified by birth weight in 500-gram increments: Findings from the Japan Environment and Children's Study.

Growth charts are essential tools for monitoring the physical development of children. We analyzed data from a nationwide Japanese birth cohort of 98,987 participants to create eight growth charts stratified by birth weight in 500-gram increments. Infants with birth weight < 2,500 g showed significant improvements in height and weight standard deviation (SD) scores by 4 yr of age. Boys and girls weighing 500-999 g at birth had average length/height SD scores of -6.40 and -8.20, which improved to -1.26 and -1.17 by 4 yr of age, respectively. Conversely, infants with birth weight ≥ 3,500 g showed decreased height and weight SD scores by 4 yr of age. Boys and girls weighing ≥ 4,000 g had average length/height SD scores of 1.87 and 2.10 at birth, which decreased to 0.34 and 0.51 by 4 yr of age, respectively. These findings reveal distinct growth patterns for different birth weight categories, highlighting the impact of birth weight on early childhood growth trajectories. The growth charts developed here serve as a valuable tool for evaluating children born small or large. These charts enable a more accurate monitoring of children's growth and can be useful in both clinical and public health settings.