In the human, large nucleated blood cells are first formed in the yolk sac and some enucleate. During the second gestational month, erythropoiesis moves to fetal liver, wherein smaller, but still macrocytic, non nucleated cells are produced. At bih, the hepatic phase of blood cell production ceases, and erythropoiesis moves to the marrow. Ref: Prchal J.T. (2010). Chapter 31. Production of Erythrocytes. In J.T. Prchal, K. Kaushansky, M.A. Lichtman, T.J. Kipps, U. Seligsohn (Eds), Williams Hematology, 8e.