Abstract
BackgroundWe aimed to describe newborn body composition and identify which anthropometric ratio (weight/length; BMI; or ponderal index, PI) best predicts fat mass (FM) and fat-free mass (FFM).MethodsAir-displacement plethysmography (PEA POD) was used to estimate FM, FFM, and body fat percentage (BF%). Associations between FFM, FM, and BF% and weight/length, BMI, and PI were evaluated in 1,019 newborns using multivariate regression analysis. Charts for FM, FFM, and BF% were generated using a prescriptive subsample (n=247). Standards for the best-predicting anthropometric ratio were calculated utilizing the same population used for the INTERGROWTH-21st Newborn Size Standards (n=20,479).ResultsFFM and FM increased consistently during late pregnancy. Differential FM, BF%, and FFM patterns were observed for those born preterm (34+0−36+6 weeks’ gestation) and with impaired intrauterine growth. Weight/length by gestational age (GA) was a better predictor of FFM and FM (adjusted R2=0.92 and 0.71, respectively) than BMI or PI, independent of sex, GA, and timing of measurement. Results were almost identical when only preterm newborns were studied. We present sex-specific centiles for weight/length ratio for GA.ConclusionsWeight/length best predicts newborn FFM and FM. There are differential FM, FFM, and BF% patterns by sex, GA, and size at birth.
Highlights
We aimed to describe newborn body composition and identify which anthropometric ratio best predicts fat mass (FM) and fat-free mass (FFM)
Body Composition at Birth A total of 1,923 mothers, who delivered at the John Radcliffe Hospital, Oxford, in the study period and were enrolled in the INTERGROWTH-21st Project, were eligible to participate in Newborn Body Composition Study (NBCS)
Testing the regression lines at the mean gestational age (GA), girls had a lower mean FFM (Po0.001) but higher mean FM/FFM ratio (P = 0.001). These results suggest that the increase in fetal weight late in pregnancy is mostly due to an increase in FFM in both sexes and that FFM is slightly higher in boys, whereas BF% is slightly higher in girls across GAs
Summary
We aimed to describe newborn body composition and identify which anthropometric ratio (weight/length; BMI; or ponderal index, PI) best predicts fat mass (FM) and fat-free mass (FFM). Associations between FFM, FM, and BF% and weight/length, BMI, and PI were evaluated in 1,019 newborns using multivariate regression analysis. Differential FM, BF%, and FFM patterns were observed for those born preterm (34+0 − 36+6 weeks’ gestation) and with impaired intrauterine growth. Weight/length by gestational age (GA) was a better predictor of FFM and FM (adjusted R2 = 0.92 and 0.71, respectively) than BMI or PI, independent of sex, GA, and timing of measurement. CONCLUSIONS: Weight/length best predicts newborn FFM and FM. There are differential FM, FFM, and BF% patterns by sex, GA, and size at birth
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