Weight/length ratio references and newborn body composition estimation at birth from a Brazilian cohort()

OBJECTIVES: The objective was to calculate weight/length (W/L) ratio values and percentiles by sex and gestational age (GA) to estimate fat mass (FM), fat-free mass (FFM) and body fat percentage (BF%) as well as to compare these indices in preterm, small (SGA), and large (LGA) for GA, stunted and wasted infants from a Brazilian cohort of newborns, comparing with the INTERGROWTH-21st. METHODS: Secondary, cross-sectional analysis of data obtained of 7427 live-born infants from the BRISA Cohort Study in the city of Ribeirão Preto, SP, Brazil in 2010. For body composition estimation, W/L ratio was used in multiple regression models. The 3rd, 50th, and 97th percentiles for W/L ratio and body composition measures (FM, FFM, and BF%) were calculated using fractional polynomial regression models. RESULTS: Average W/L ratio was 6.50 kg/m (SD 0.87), while for FM, BF%, and FFM the corresponding values were 359.64 g (145.76), 10.90% (3.05) and 2798.84 g (414.84), respectively. SGA (< 3rd percentile), and wasted infants showed the lowest W/L ratios and measures of body composition. The 3rd, 50th, and 97th percentiles charts of W/L, FM, BF%, and FFM by GA and sex are presented. CONCLUSIONS: W/L ratio values of the RP-BRISA Cohort are higher than IG-21st. SGA (< 3rd) and wasted infants showed the lowest W/L ratio and measures of body composition. The body composition references presented here could be used to refine the nutritional assessment of Brazilian newborns and to facilitate comparisons across populations.