Body composition at birth and its relationship with neonatal anthropometric ratios: the newborn body composition study of the INTERGROWTH-21(st) project.

Background 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). Methods Air-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-21(st) Newborn Size Standards (n=20,479). Results FFM 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 R(2)=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. Conclusions Weight/length best predicts newborn FFM and FM. There are differential FM, FFM, and BF% patterns by sex, GA, and size at birth

Differences in body composition between infants of South Asian and European ancestry: the London Mother and Baby Study.

BACKGROUND: South Asian children and adults have a more adipose body composition compared with those of European ancestry. This is thought to be related to their increased risk of metabolic disorders. However, little is known about how early in life such differences are manifest. OBJECTIVE: To determine whether there are differences in fat mass (FM) and fat-free mass (FFM) between UK-born South Asians and White Europeans in infancy. Design A cross-sectional study of 30 South Asian and 30 White European infants aged 6-12 weeks. Mothers were recruited from clinics in London, and infants' FM and FFM were determined using air-displacement plethysmography (PeaPod(®)). RESULTS: In early infancy South Asians had less FFM than White Europeans [0.34 kg less, 95% confidence interval (CI): 0.15, 0.52], with a considerably weaker indication of them also having more FM (0.02 kg more, 95% CI: -0.14, 0.18). These differences persisted when the overall smaller body size of South Asian infants was taken into account. For a given total infant weight, the balance of body composition of South Asians was shifted by 0.16 kg (95% CI: 0.06, 0.25) from FFM to FM. The ethnic differences in the amount of FFM were almost completely accounted for by ethnic differences in the rate of growth in utero and length of gestation. CONCLUSIONS: The characteristic differences in body composition observed between adult South Asians and White Europeans are apparent in early infancy. Of particular note is that this is the first study to demonstrate that South Asians compared with White Europeans have reduced FFM in infancy. The early manifestation of this phenotype suggests that it is either genetic and/or determined through exposure to maternal physiology, rather than a consequence of behaviours or diet in childhood or at older ages