Measurement of human fetoplacental blood volume in erythroblastosis fetalis.

The fetoplacental blood volume of the human fetus was measured with the change in hematocrit at the time of intravascular transfusion for severe erythroblastosis. A total of 121 measurements were made between 18 and 31 weeks' gestation. The volume ranged from 117 ml/kg at 18 weeks to 93.1 ml/kg at 31 weeks. These values compare closely with those reported for the sheep fetus and, when they are extrapolated to term, are similar to the blood volume of human newborns plus the residual placental blood volume.