Nucleated red blood cells, aka normoblasts or erythroblasts, were released prematurely from the bone marrow in these newborns because of hypoxia. The arrow points to a polychromatophilic normoblast. The other nucleated cells are orthochromic normoblasts.

In the fetus/newborn the causes of hypoxia are many and varied, including Rh incompatibility and ABO incompatibility. Normal maturation of red cell precursors to mature erythrocytes goes through several stages; proerythroblast – basophilic normoblast – polychromatophilic normoblast – orthochromic normoblast – reticulocyte – mature.

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