Weight loss in full-term negroid infants: relationship to body water compartments at birth?

The possible influence of the body fluid compartments at birth on postnatal weight loss was studied in normal term negroid infants when on a standardized oral fluid, sodium and energy regimen during the first three days of life. Measurements of plasma volume (PV), total body water (TBW), and extracellular water (ECW) were performed simultaneously on vaginally-born infants on the first day of life, by using a triple indicator (Evans blue, deuterium oxide and sucrose) single injection dilution technique. PV was 54 +/- 7 ml/kg (N = 9), TBW was 751 +/- 50 ml/kg (N = 13) and ECW was 311 +/- 61 ml/kg (N = 13) (mean +/- S.D.). Postnatal weight loss (3.7% of birth weight) occurred during the first two days. The postnatal weight loss was not related to any of the body water compartments. However, there was a highly significant correlation with the (cumulative) urine water excretion (r = 0.833, P less than 0.001 on day 1, with similar values for days 1 and 2).