The use of bioelectrical impedance analysis in newborns. The need for standardization.

Rapid growth occurs during fetal and neonatal development. The duration and quality of intrauterine development affect neonate body composition. Weight is routinely used to assess and monitor the nutritional status of newborns. Any weight loss or gain in hospitalized newborn infants may reflect shifts in water balance rather than changes in body mass, and have strong implications for investigating the nutritional status of newborns. It is, however, difficult to measure the body composition of newborns. Bioelectrical impedance analysis (SIA) is a relatively new technique for estimating body composition. It is based on the fact that the conduction of an applied electrical signal is far greater in fat-free tissues (because of water and electrolyte content) than in fat. BIA has been gaining wide usage for the estimation of body composition in adultsl.2, and should be a very suitable method for use in children, because of its noninvasiveness, simplicity and reliability. No mathematical equation can be applied to young children to transform BIA results into body composition variables. Calculation of the lean and fat content from measurement of body weight and BIA implies a constant relation between body water and lean body mass, but present measurements in neonates do not support this assertion. Few studies using BIA have been performed in newborns. A relation between Iengthz/R and the volume of body water has been postulated in the newborn38. Assuming this relation to be true, BIA measurements provide a useful tool in perinatal body water and nutrition studies. The purposes of our study with newborns were to determine the reliability of the method, to show the influence of electrode position on the result and to compare and contrast the anthropometric and BIA status of smallor appropriate-forgestational-age newborns at birth and at 3 weeks of age.