Extramedullary hematopoiesis is very common in the human fetus. At 8 months' gestation, the most impoant site of hematopoiesis is the:

The first site of hematopoiesis in the fetus is the yolk sac. By 3 months gestation, the liver makes the largest contribution. However, by the eighth month the marrow is the most impoant site. Fetal blood at that point has a very high Hb F concentration. As term approaches, the erythrocytes also contain less Hb F than they do early in pregnancy. Ref: Adamson J.W. (2012). Chapter 103. Iron Deficiency and Other Hypoproliferative Anemias. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.