During first 3-4 month of gestation erythrocytes are formed by
High-Yield Explanation
A i.e. Yolk sac; B i.e. Liver; C i.e. Spleen Erythropoiesis (blood production) occurs in mesodermal wall of yolk sacQ (i.e. intravascular) from 3 weeks to 3 months of gestation and in liver > spleen & lymph nodesQ (hepatic extramedullary) from 2 months to 7 months of gestation. After this erythropoiesis occurs in marrow (myeloid tissue).