Nonlinear Physical Growth of Children from Infancy to Middle Adolescence in Low- and Middle-Income Countries

Background: The growth curve has a significant role in understanding the growth trajectories overtime and examining the mathematical relationship between the outcome variable and time.Study design: A longitudinal prospective cohort study.Methods: This study aimed to identify a nonlinear growth curve that best represents the growthtrajectories in children’s physical growth from ages ۱ to ۱۵ years. The data were obtained from theYoung Lives study conducted in Ethiopia, India, Peru, and Vietnam. Nonlinear growth curves werestudied through the families of three-parameter nonlinear mixed-effects models.Results: The study examined the performances of different three-parameter nonlinear growthcurves for the growth trajectory analysis, and the Logistic curve was chosen for the trajectoryanalysis. Gender and country differences had significant effects on the child’s growth. Femalesreached asymptotic height earlier and shorter than males. The mean height values at the end ofthe growth stage for children in Ethiopia, India, Peru, and Vietnam were ۱۷۱.۷۸, ۱۷۰.۳۷, ۱۷۱.۳۰,۱۷۴.۳۱cm, respectively. Children in Ethiopia approached adult height earlier than those in India butlater than children in Peru. However, no significant growth change was observed between childrenin Ethiopia and Vietnam. This indicates that children in Ethiopia and Vietnam have no significantdifferences regarding approaching adult height.Conclusion: The study concludes that the Logistic curve was found to be the best growth curve todescribe the growth trajectories. Children in all four countries exhibited different growth parameters.