Comparison of Chinese and international birth weight standards in predicting early childhood growth outcomes: a retrospective cohort study.

Background: Birth weight serves as a key predictor for long-term health trajectories. Currently, both international and Chinese standards are used to evaluate birth weight. This study aims to compare the Chinese Newborn Growth Standards (CNGS) and the INTERGROWTH-21st (IG-21) standards in terms of birth weight classification and their predictive performance for the wasting and possible risk of overweight during infancy and toddlerhood. Methods: This retrospective cohort study included 1,149 full-term singleton infants with longitudinal growth data recorded at 1, 2, and 3 years of age. Birth weight was categorized according to both the CNGS and IG-21 standards. Wasting and possible risk of overweight during infancy and toddlerhood were assessed according to World Health Organization (WHO) standards. Agreement between the two classification systems was evaluated using the weighted Kappa statistic. The predictive performance of each standard for growth outcomes was compared using modified Poisson regression models. Results: The CNGS and IG-21 standards showed high agreement (Kappa = 0.856). In terms of predictive performance, based on the CNGS, small for gestational age (SGA) was significantly associated with wasting at 1 and 2 years, and large for gestational age (LGA) was significantly associated with possible risk of overweight at 2 years. In contrast, based on the IG-21 standards, only SGA showed a significant association with wasting across all follow-up ages. Overall, the CNGS demonstrated higher specificity in predicting wasting and possible risk of overweight in infants and toddlers. Conclusion: Although the CNGS and IG-21 standards showed high agreement, the CNGS demonstrated superior predictive validity for growth outcomes during infancy and toddlerhood, particularly for possible risk of overweight.