During which week of gestation does red bone marrow begin to produce blood cells?

Red bone marrow begins to produce blood cells around the 20th week of gestation, marking a significant developmental milestone in fetal hematopoiesis. Prior to this stage, blood cell production occurs primarily in the yolk sac and the liver. At approximately 20 weeks, the transition to red bone marrow as the primary site for blood cell formation is established, indicating that the skeletal system is developing sufficiently to support this function. This process is crucial for providing the growing fetus with the necessary red blood cells to carry oxygen and nutrients effectively.