Nutritional assessment and measurement of body composition in preterm infants.

To compose an optimal nutrition for preterm infants, it is necessary to assess their body composition and metabolism. Much information on body composition has become known by carcass analysis of stillborn (pre)term infants, but these data do not inform us about the rapid alterations in body composition of surviving preterm infants during the first weeks of life. Many noninvasive nutritional assessment techniques have been developed with special adaptation to preterm infants. With these techniques it is now possible to have an accurate assessment of TBW, extracellular water; total body fat; fat-free mass; bone mineral content; energy expenditure (metabolic rate); and energy substrate turnover. Most of these techniques unfortunately show relatively large intraindividual variations and, in most cases, it is only possible to study and compare groups of preterm infants. Studies of individual patients over a certain period of time are still rather inaccurate.