After a bone marrow (stem cell) transplant, it generally takes 10 to 15 days for the transplanted stem cells to begin producing new blood cells. During this period, external blood cell supplements, such as red blood cells and platelets, are provided to support the patient's blood count. These transfusions will be necessary until the transplanted bone marrow starts producing a sufficient number of healthy blood cells on its own. It is critically important for patients to attend regular follow-up appointments and undergo blood tests to assess the response to the transplant and monitor for potential complications. To prevent serious post-transplant issues and ensure long-term health, patients may require meticulous follow-up for many years.