09/20/2012 11:47 am ET

Bone Marrow Transplant: What Is The Procedure Robin Roberts Is Undergoing For Myelodysplastic Syndrome?

"Good Morning America" co-anchor Robin Roberts, 51, is undergoing a bone marrow transplant today (Sept. 20), months after announcing her diagnosis with the rare blood disorder myelodysplastic syndrome, according to news reports.

She has been in the hospital for 11 days already, eight of which were spent undergoing chemotherapy that is necessary to prepare for the transplant, People magazine reported.

Robin Roberts wrote in a tweet yesterday:

Myelodysplastic syndrome, formerly known as preleukemia, is a condition where the bone marrow does not produce enough healthy blood cells, according to the National Cancer Institute. Common treatments include medication and bone marrow transplant, like the one Roberts will undergo.

With a bone marrow transplant, the patient first undergoes chemotherapy so that the body's defective blood cells are destroyed, according to the Mayo Clinic. Then, those cells are replaced by either a person's own stem cells (called an autologous transplant), or a donor's, which is called an allogeneic transplant. In Roberts's case, she is receiving bone marrow stem cells from her sister, who was found to be a match.

The National Institutes of Health reported that the actual transplantation usually does not require surgery; the donor's stem cells are delivered to the patient's body via a central venous catheter. Then, those cells go to the bone marrow, which is the sponge-like tissue in bone.

The patient's blood cell count will begin to rise when these donated cells start to grow and go on to produce new blood cells, according to the National Marrow Donor Program.

But until the immune system gets to full strength again, the patient must be watched carefully by doctors for the 100 days following the transplant because of complication risk, the National Marrow Donor Program reported. That's because post-transplant, the immune system is still weak and infections may occur. Other possible complications include acute graft-versus-host disease, which is when the donated cells attack the body, and graft failure, which is when the donated cells are rejected by the body.

People can become marrow donors by registering with the Be the Match Registry. According to the most recent registry data, transplants that were conducted via donors from this registry increased between 2005 and 2010, from 2,600 to 5,200.

In 2010, 15 percent of these transplants from donors were conducted in patients with myelodysplastic syndromes, according to the registry data.

Want to sign up to be a bone marrow donor? Click here for more information about Be the Match.