Stable isotopes and bioelectrical impedance for measuring body composition in infants born small for gestational age

The assessment of body composition in infants born small for gestational age (SGA) is required primarily to evaluate nutritional status and to monitor growth in the neonatal period. Measurement of total body water, using stable isotopes of hydrogen (H-2) and oxygen (O-18), offers a potential method by which body composition can be assessed. This technique is non-invasive and recently has been used successfully in a cohort of 5-week-old infants born SGA. Nevertheless, the assessment of total body water using stable isotopes requires specialized laboratories and equipment, which may limit its use. Prediction of total body water by bioelectrical impedance is a possible alternative. This technique uses electrical theory to predict the volume of the conducting medium in the body, namely, water. A potential limitation of bioelectrical impedance analysis is the accuracy, which may impinge on its usefulness in small infants.