Classification of weight status in infancy and obesity prediction according to weight-for-length and body mass index

Objective Weight-for-length (WFL) is recommended for assessing weight status in infants under 2 years, although body mass index (BMI) may be an alternative. We compared weight classifications using WFL and BMI and assess their ability to predict later obesity. Study Design: This longitudinal study analysed public health data from Calgary, Canada (2000–2018). Growth measures from full-term infants under 2 years and children aged approximately 4.5 years were assessed using World Health Organization growth standards. Classification agreement and predictive performance were examined. Results Among 191,956 children, 51% were male. WFL and BMI showed moderate-to-strong agreement. Areas under the receiver operating characteristic curve for predicting later overweight and obesity ranged from 67.7%–79.2% for BMI and 65.7%–80.0% for WFL. Infant overweight/obesity classifications (> 2 z-scores) poorly predicted later status. Conclusion BMI and WFL showed comparable classification and predictive performance. Further research should evaluate BMI-based infant growth monitoring.