Summary
Inulin and PAH clearances, urine flow, filtration fraction, electrolyte excretion and blood volume studies were performed on 43 term vaginally delivered female normal infants during the first 12 hours of life and 26 during the 2nd to the 5th day of age. The umbilical cords of 22 infants were clamped within 5 seconds after birth and in 47 infants, the cords were clamped after their arterial pulsation had stopped.
Compared with the late clamped infants, the blood volume, red cell volume and venous hematocrit were lower in the early clamped infants during the first five days of life. The urine flow, glomerular filtration rate (GFR), PAH clearance and effective renal blood flow were also lower in the early clamped infants during the first 12 hours of life, presumably due to the lower blood volume and blood pressures. At 2‐5 days of age, the urine flow, GFR, PAH clearance and effective renal blood flow were the same in both groups of infants in spite of persistent difference in blood volume. The early clamped infants apparently achieved renal adaptation through means other than blood volume compensation.
Data on electrolyte metabolism suggest that the late clamped infants filtered and reabsorbed larger amount of sodium than the early clamped infants during the first 6 hours of life, accompanied by a greater urine flow. These findings were appropriately achieved by the kidney in the process of body fluid regulation in response to the vascular distension and fluid transudation resulting from placental blood transfusion at birth.