Body composition of preterm infants measured during the first months of life: bioelectrical impedance provides insignificant additional information compared to anthropometry alone

Detailed knowledge of body composition in preterm neonates during their later postnatal period may be important for the treatment process. However, little consideration has been given to test whether bioelectrical impedance analysis (BIA) is a useful bedside method to predict fat-free mass (FFM). The aim of the study is to assess whether BIA is a bedside method to measure FFM in preterm neonates. FFM of 118 white subjects (51 mates, 67 females), mean gestational age of 30.1 +/- 3.1 weeks and birth weight of 1.26 +/- 0.47 kg, was measured at a gestational age of 38.6 +/- 3.8 weeks and actual body weight of 2.6 +/- 0.54 kg using dual energy X-ray absorptiometry (FFMDXA). Weight (W), height (Ht), and bioelectric impedance (I) measurements were collected. Multiple regression analysis was performed to develop prediction equations to estimate FFM with impedance index (Ht(2), cm(2)/Omega) and W (kg) as predictor variables. Bootstrap analysis was performed for validating the derived prediction equations. Correlations between FFMDXA and weight were 0.96, 0.98, and 0.97 in boys, girls, and both sexes, respectively. Those between FFMDXA and He/I were: 0.13, 0.81, and 0.79. Equations used to predict FFM (kg) were for boys: FFM = 0.05Ht(2)/I + 0.68W + 0.40(R-2 = 0.919) and for girls: FFM = 0.04Ht(2)/I + 0.71 W + 0.29(R-2 = 0.957). Conclusions. In preterm neonates, weight is a more effective predictor of FFM than impedance index. The study provides a bedside procedure for estimating FFM, mainly based on anthropometric parameters rather than BIA.