Nonlinear Catch-Up Growth in Height, Weight, and Head Circumference from Birth to Adolescence: A Longitudinal Twin...

Owing to high rates of prenatal complications, twins are, on average, substantially smaller than population norms on physical measurements including height, weight, and head circumference at birth. By early childhood, twins are physically average. This study is the first to explore the process of catch-up growth by fitting asymptotic growth models to age-standardized height, weight, and head circumference measurements in a community sample of twins ( n  = 1,281, 52.3% female) followed at up to 17 time points from birth to 15 years. Catch-up growth was rapid over the first year and plateaued around the population mean by early childhood. Shared environmental factors accounted for the majority of individual differences in initial physical size (57.7%-65.5%), whereas additive genetic factors accounted for the majority of individual differences in the upper asymptotes of height, weight, and head circumference (73.4%-92.6%). Both additive genetic and shared environmental factors were associated with variance in how quickly twins caught up. Gestational age and family SES emerged as important environmental correlates of physical catch-up growth.