Body water content of extremely preterm infants at birth

Background-Preterm birth is often associated with impaired growth. Small for gestational age status confers additional risk. Aim-To determine the body water content of appropriately grown (AGA) and small for gestational age (SGA) preterm infants in order to provide a baseline for longitudinal studies of growth after preterm birth. Methods-All infants born at the Hammersmith and Queen Charlotte's Hospitals between 25 and 30 weeks gestational age were eligible for entry into the study. Informed parental consent was obtained as soon after delivery as possible, after which the extracellular fluid content was determined by bromide dilution and total body water by (H2O)-O-18 dilution. Results-Forty two preterm infants were studied. SGA infants had a significantly higher body water content than AGA infants (906 (833-954) and 844 (637-958) ml/kg respectively; median (range); p = 0.019). There were no differences in extracellular and intracellular fluid volumes, nor in the ratio of extracellular to intracellular fluid. Estimates of relative adiposity suggest a body fat content of about 7% in AGA infants, assuming negligible fat content in SGA infants and lean body tissue hydration to be equivalent in the two groups. Conclusions-Novel values for the body water composition of the SGA preterm infant at 25-30 weeks gestation are presented. The data do not support the view that SGA infants have extracellular dehydration, nor is their regulation of body water impaired.