Importance: The American Academy of Pediatrics currently recommends weight-for-length (WFL) for assessment of weight status in children <2 years, but body mass index (BMI) for children above 2 years. Yet the clinical implications of using WFL vs BMI in children <2 years as a predictor of future health outcomes remains understudied.
Objective: To compare associations of overweight based on WFL vs BMI in children <2 years with cardio-metabolic outcomes in early adolescence.
Design: Prospective study of two birth cohorts in United States (Project Viva) and Belarus (Promotion of Breastfeeding Intervention Trial, PROBIT)
Main exposure: Overweight by Centers for Disease Control and Prevention (CDC) WFL≥95th percentile, World Health Organization (WHO) WFL ≥97.7th percentile or WHO BMI ≥97.7th percentile at 6, 12, 18 or 24 months
Main outcomes and measures: Fat-mass index, insulin resistance, metabolic risk score, obesity (primary outcomes); height and body mass index z-scores, sum of skinfolds, waist circumference, systolic blood pressure (secondary outcomes) in early adolescence
Results: Our analysis included 919 (50.1% male, 65.1% white ethnicity) children from Project Viva and 12747 (48.7% male, 100% white ethnicity) from PROBIT. During 6‒24 months, 22.4%, 17.4% and 17.5% of children in Project Viva, and 29.1%, 24.1% and 24.5% of children in PROBIT, were overweight at any of the four timepoints using CDC WFL, WHO WFL and WHO BMI cut-points, respectively. After adjusting for maternal and child characteristics, being ever overweight (vs. never overweight) during 6‒24 months of age was associated with higher likelihood of adverse cardio-metabolic risk markers in early adolescence, yet associations did not differ greatly across WFL and BMI cut-points in either cohort [e.g. for fat-mass index (in kg/m2) Project Viva ‒ CDC WFL: β 0.9 (95% CI 0.5,1.4); WHO WFL: 1.1 (0.6,1.6); WHO BMI: 1.4 (0.9,1.9); PROBIT ‒ CDC WFL: 0.5 (0.4,0.6); WHO WFL: 0.6 (0.5,0.7); WHO BMI: 0.6 (0.5,0.6)]. Neither growth metric in infancy was superior over the others, based on F-statistics. Findings were similar for insulin resistance, metabolic risk score, obesity and secondary outcomes.
Conclusions: Choice of WFL vs. BMI to define overweight in the first 2 years of life does not greatly affect the associations with cardio-metabolic outcomes in early adolescence.