The definition of postpartum hemorrhage is bleeding greater than 500 milliliters approximately 24 hours after vaginal delivery. Whether blood transfusion is necessary for postpartum hemorrhage mainly depends on the specific amount of bleeding. For average women, if the hemoglobin level is normal before delivery and the bleeding is between 500-1000 milliliters, the body can compensate for the anemia through normal adjustments, and generally, a blood transfusion is not required. However, if the bleeding exceeds 1000 milliliters, this situation is considered massive hemorrhage and must be treated with a blood transfusion, otherwise it may lead to hemorrhagic shock or DIC (Disseminated Intravascular Coagulation).