The following are related to fetal erythropoiesis except :

Primitive hematopoiesis and vasculogenesis first occur in the yolk sac followed by liver and finally bone marrow, leading to the production of blood and vessels respectively Blood islands, clusters of primitive erythrocytes surrounded by endothelial cells, arise from the extraembryonic mesoderm in the yolk sac Hematopoiesis (formation and development of various types of blood cells) begins in the liver during the sixth week The first erythrocytes released into the fetal circulation are nucleated and macrocytic Hemoglobin content of fetal blood rises to approximately 12 g/dL at midpregnancy and to 18 g/dL at term Because of their large size, fetal erythrocytes have a sho lifespan, which progressively lengthens to approximately 90 days at term Erythropoiesis is controlled primarily by fetal erythropoietin because maternal erythropoietin does not cross the placenta Fetal blood is first produced in the yolk sac, where hemoglobins Gower 1, Gower 2, and Poland are made Erythropoiesis then moves to the liver, where fetal hemoglobin F is produced When hemopoiesis finally moves to the bone marrow, adult type hemoglobin A appears in fetal red blood cells and is present in progressively greater amounts as the fetus matures The final adult version of the a chain is produced exclusively by 6 weeks. After this, there are no functional alternative versions Reference: William's Obstetrics; 24th edition; Chapter 7