Body water content of extremely preterm infants at birth

Background-Preterm birth is often associated with impaired growth. Small fo r gestational age status confers additional risk. Aim-To determine the body water content of appropriately grown (AGA) and sm all for gestational age (SGA) preterm infants in order to provide a baselin e 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 s tudy. Informed parental consent was obtained as soon after delivery as poss ible, 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 significa ntly 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 differe nces in extracellular and intracellular fluid volumes, nor in the ratio of extracellular to intracellular fluid. Estimates of relative adiposity sugge st a body fat content of about 7% in AGA infants, assuming negligible fat c ontent in SGA infants and lean body tissue hydration to be equivalent in th e 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 regulati on of body water impaired.