Fetal polycythemia and hyperviscosity: effect on umbilical blood flow and fetal oxygen consumption.

To evaluate the effect of fetal polycythemia and hyperviscosity on fetal oxygen transport, we induced those conditions in eight chronically instrumented fetal lambs by isovolemic exchange transfusion with packed red cells obtained from a donor ewe. This procedure resulted in polycythemia and hyperviscosity without altering fetal arterial blood oxygen content. The fetuses were studied at 1 and 48 hours after polycythemia and hyperviscosity. In spite of decreased oxygen delivery to the fetus, the fetal oxygen consumption was unchanged because of an increase in oxygen extraction by the fetus.