Growth and body composition trajectories in infants meeting the WHO growth standards study requirements.

BACKGROUND: While the World Health Organization (WHO) developed postnatal growth standards for infants, corresponding body composition data remains scarce. This study explores growth and body composition trajectories in infants meeting the WHO Multicentre Growth Reference Study (MGRS) eligibility criteria. STUDY DESIGN: Infants enrolled in this longitudinal cohort underwent anthropometric and body composition measurement by air displacement plethysmography (ADP) at 6 weeks, 12 weeks, and 5 months postnatally. Age and sex-specific growth and body composition percentiles were generated using GAMLSS, with extrapolated data at 5 months for those exceeding ADP weight limits. We evaluated which anthropometric measure (body mass index (BMI), weight for length or mid upper arm circumference) was most closely related to adiposity. RESULTS: Of the 225 infants with body composition measures, 187 met the WHO MGRS criteria. Their length and weight curves were comparable with WHO growth curves. Trajectory curves for fat and fat-free mass were developed. Of the anthropometric measures, BMI z score was most closely related to fat mass index z score at all timepoints. CONCLUSION: This study presents body composition trajectories for infants meeting the WHO growth standard criteria. BMI z score is the best anthropometric metric to estimate adiposity in infants. IMPACT: While postnatal growth standards derived from the WHO Multicentre Growth Reference Study (MGRS) exist for the routine clinical assessment of infant growth, this study fills the previous gap in the availability of corresponding body composition data for term-born, healthy, breastfed infants meeting the MGRS criteria. Extrapolation was used to obtain body composition values for infants exceeding the weight limit of the ADP device, to avoid construction of biased body composition curves. Sex-specific growth curves for fat mass, fat-free mass, fat mass index, and fat-free mass index are presented for a population meeting the World Health Organization growth standard criteria.