Nucleated red blood cells in the fetus and newborn.

Although nucleated red blood cells (nRBCs) are rarely found circulating in older children, they are commonly seen in the blood of newborns. They are primarily produced in the fetal bone marrow in response to erythropoietin and are stored in the marrow as precursors to reticulocytes and mature erythrocytes. Many acute and chronic stimuli cause increases in the number of circulating nRBCs from either increased erythropoietic activity or a sudden release from the marrow storage pools. This paper reviews the various pathological processes associated with increased production and release of nRBCs. It emphasises the eVects of acute, subacute, and chronic asphyxia on nRBC counts. Nucleated red blood cells are sometimes called erythroblasts, normoblasts, or normocytes. For this review, the term “normoblasts” will be used to refer to the cells when they are in the bone marrow and “nRBCs” when they are in circulating blood.