Fetal plasma erythropoietin concentration in red blood cell-isoimmunized pregnancies

The aim of this study was to investigate the relationship between fetal anemia, plasma erythropoietin concentration, and erythroblastosis in red blood cell-isoimmunized pregnancies.

Fetal plasma erythropoietin concentration in umbilical venous blood samples from 68 red blood cell-isoimmunized pregnancies at 18 to 35 weeks' gestation was measured. Measurements were compared with the appropriate reference range with gestation, and associations with blood pH, erythroblast count, and hemoglobin concentration were examined.

The mean fetal plasma erythropoietin concentration and erythroblast count in red blood cell-isoimmunized pregnancies were significantly increased only in severe fetal anemia (hemoglobin deficit > 7 gm/dl). Furthermore, some severely anemic fetuses were hydropic and acidemic. The degree of increase in plasma erythropoietin was significantly associated with both fetal acidemia and, more strongly, fetal erythroblastosis.

These findings suggest that in fetuses from red blood cell-isoimmunized pregnancies the ability to prevent tissue hypoxia is present until anemia becomes severe, presumably by an increase in cardiac output and tissue perfusion. In severe anemia tissue hypoxia occurs, and the data indicate that fetuses respond by increasing erythropoietin production from at least 20 weeks' gestation. Furthermore, more accurate assessment of tissue oxygenation may be obtained by measuring the erythroblast count rather than the blood pH.