Accurate assessment of neonatal body composition is essential to studies investigating neonatal nutrition or developmental origins of obesity. Bioelectrical impedance analysis or bioimpedance analysis is inexpensive, non-invasive and portable, and is widely used in adults for the assessment of body composition. There are currently no prediction algorithms using bioimpedance analysis in neonates that have been directly validated against measurements of fat-free mass (FFM). The aim of the study was to evaluate the use of bioimpedance analysis for the estimation of FFM and percentage of body fat over the first 4 months of life in healthy infants born at term, and to compare these with estimations based on anthropometric measurements (weight and length) and with skinfolds. The present study was an observational study in seventy-seven infants. Body fat content of infants was assessed at birth, 6 weeks, 3 and 4·5 months of age by air displacement plethysmography, using the PEA POD body composition system. Bioimpedance analysis was performed at the same time and the data were used to develop and test prediction equations for FFM. The combination of weight þ sex þ length predicted FFM, with a bias of , 100 g and limits of agreement of 6-13 %. Before 3 months of age, bioimpedance analysis did not improve the prediction of FFM or body fat. At 3 and 4·5 months, the inclusion of impedance in prediction algorithms resulted in small improvements in prediction of FFM, reducing the bias to ,50 g and limits of agreement to ,9 %. Skinfold measurements performed poorly at all ages.

Infant body composition is affected by maternal obesity, which results in increased % body fat in the infant. With the rapidly increasing incidence of obesity, it is important that normative data are available for infant body composition that is not affected by this trend in maternal obesity. This study assessed body composition in infants born at term to women with a BMI between 18.5 and 25. Infant % body fat, fat mass (FM), and fat free mass (FFM) were assessed at birth, 6 wk, 3 mo, and 4.5 mo of age by air displacement plethysmography, using the PEA POD body composition system. The effects of age, gender, GA, and feeding mode on these parameters were assessed. The % body fat doubled between birth and 6 wk of age and then increased at a slower rate. FFM was higher in male infants at all ages, whereas % body fat was higher in female infants at 4.5 mo. There was a trend to increased % fat and decreased FFM in breastfed (BF) infants. The study provides unique data regarding changes in infant body composition and growth in infants born to women in the healthy weight range. (Pediatr Res 68: 84-88, 2010) B ody composition in early life may play a key role in the programming of a variety of health outcomes, including hypertension, stroke, type 2 diabetes, obesity, and cardiovascular disease (1). The Barker hypothesis states that undernutrition and small size at birth are associated with increased risk of cardiovascular disease and type 2 diabetes later in life (2). Observational evidence also suggests that faster growth during infancy is associated with an increased risk of obesity (2-5). This is an area of very active research, and in this environment, it is important to establish normal values for infant body composition and growth. In addition, the assessment of feeding interventions for preterm infants may be improved by measuring changes in fat free mass (FFM) vs. fat mass (FM). Deviations from normal developmental patterns of body composition may program these infants for later health problems (2-5). Again, it is critical that normative data be established for infant body composition.Historically, growth has been monitored by serial measurements of weight, length, and head circumference, with little information available on the compositional nature of infant growth. Early data were based on chemical analysis of a small number of stillborn infants (6,7). More recently, body composition has been measured using dual-energy x-ray absorptiometry (DXA) (8,9), total body electrical conductivity (TOBEC) (10), magnetic resonance imaging (11), or multicompartment models based on total body water, total body potassium, and bone mineral content measurements (12). However, many of these studies did not measure body composition at birth, and no studies have taken maternal body composition into account. Because it has been shown that maternal overweight/obesity is associated with increased body fat in the newborn infant (13,14), and the prevalence of maternal obesity is increasing, there is a need to establish norma...

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