What is a cord blood transplant, and how does it work?

After a baby is born, the umbilical cord is clamped and cut as usual. Some blood is left in the cord and placenta. This cord blood is rich in blood-forming stem cells, the young cells that grow into red cells, white cells and platelets. If it is not donated, it is usually thrown away with the placenta.

A cord blood transplant gives those cells to a patient through a vein, the same way as other stem cell transplants. It is a kind of allogeneic, or donor, transplant. The first successful one was done in Paris in 1988, for a 5-year-old boy with Fanconi anemia. By the end of 2019, about 35,000 had been done worldwide.

Public cord blood banks test and freeze donated units. Units that qualify are listed on donor registries, where transplant teams can search them. Each unit is known only by a number, never by a name. A patient who receives cord blood has no direct contact with the family who donated it.

Doctors match patients and donors using HLA, the tissue-type markers found on most cells. With an adult volunteer donor, teams look for a very close match. Cord blood is more forgiving. US guidelines from NMDP, which runs the national registry, and CIBMTR, a transplant research group, say cord blood tolerates more HLA mismatch.

Matching still matters. The same guidelines say units matched at fewer than 4 of 8 HLA markers are generally avoided. Teams also weigh how many cells a unit holds and the quality of the unit.

People are most likely to match a donor of similar ancestry, because HLA genes are inherited. Some groups have fewer volunteers on the registry. Because a partial match can work, NMDP calls cord blood especially promising for patients from diverse backgrounds. A 2014 study of the US registry found cord blood units with one or two mismatches for almost all patients under 20. It found them for more than 8 in 10 patients aged 20 or older, whatever their background.

An adult volunteer has to be contacted, checked and scheduled before donating, which can take weeks or months. A cord blood unit has already been collected, tested and frozen. Guidelines published in 2025 by NMDP and CIBMTR list its rapid and predictable availability as a main advantage.

Speed matters most when an illness moves fast. Infantile Krabbe disease is a rare inherited disease that harms the nervous system in early childhood. A 2005 US study followed 25 babies who received unrelated cord blood. Babies treated at 12 to 44 days old, before symptoms began, did much better than babies treated after symptoms started. Some still had delays in movement or speech.

Hurler syndrome (MPS I) is a rare inherited storage disease that affects many organs in early childhood. A 2011 European expert consensus said survival and engraftment after transplant had improved a great deal. It named three main reasons: guidelines that include unrelated cord blood as a cell source, careful dosing of chemotherapy, and a short gap between diagnosis and transplant.

One cord blood unit holds far fewer stem cells than a donation from an adult. A 2017 review put it at typically about 5% to 10% of the cells in a blood or marrow donation. So the new cells usually take longer to settle in the marrow and start making blood. This is called engraftment.

The same review summarized the timing after full-strength conditioning. White cells called neutrophils usually recovered in about 20 to 30 days with cord blood. That compared with about 10 to 20 days with stem cells from an adult’s blood, and 15 to 25 days with marrow. Until the new cells take hold, blood counts stay low. The risk of infection and of the graft being rejected is higher.

The small number of cells is a particular problem for adults. When no single unit has enough cells, some centers give two units together. This is called a double cord blood transplant.

Researchers have also looked for ways to grow more cells. In April 2023, the US Food and Drug Administration (FDA) approved omidubicel (Omisirge) for people 12 and older with blood cancers. It is cord blood that has been grown in a lab with nicotinamide, a form of vitamin B3. In its main trial of 125 people aged 12 to 65, neutrophils recovered in a median of 12 days, compared with 22 days with standard cord blood. The FDA has since approved it for severe aplastic anemia in people 6 and older. Like all approved cord blood products, its label warns of serious risks, including graft-versus-host disease and graft failure.

Cord blood has been used for blood cancers such as leukemia and lymphoma, and for other serious conditions. The American Academy of Pediatrics describes it as a treatment option for infants, children and adults. It lists certain blood cancers, hemoglobin disorders, severe immune deficiencies and metabolic diseases. NMDP names sickle cell disease among the conditions it can treat.

Its role has changed. Half-matched family transplants became much safer with a method called post-transplant cyclophosphamide (PTCy), and cord blood is now used less often. Among donor transplants reported to the EBMT, a European transplant group, for 2024, about 1 in 100 used cord blood. Its use kept falling.

US guidelines published in 2025 found no benefit of cord blood over other partly matched donors for adults with blood cancers when PTCy is used. They say it should be kept for centers with special cord blood expertise, clinical trials or carefully chosen patients.

Not every expert agrees. A 2026 review by UK transplant specialists argues that cord blood still deserves a place. It points to survival comparable to other sources and a strong effect against leukemia. It also points to less long-term graft-versus-host disease (GVHD), when donor immune cells attack the patient’s body. The transplant team weighs these options for each patient.

Parents can donate cord blood to a public bank. It is collected only after the baby is born and the cord has been clamped and cut. NMDP says labor and delivery are not affected, and there is no extra recovery time for mother or baby. It also says there is no cost to donate to a public bank.

Donation needs planning, because not every hospital collects cord blood. In the United States, NMDP works with cord blood banks in 19 states. Parents check whether their delivery hospital takes part, then contact the bank to see if they can donate. NMDP suggests contacting a public bank as early as possible. It says some families may be able to take part through a mail-in program instead. In the UK, the charity Anthony Nolan collects cord blood at five hospitals in London, Manchester and Leicester.

Many donations are never used for a transplant. Units need enough cells to be stored. The American Academy of Pediatrics reported in 2017 that only about 25% to 40% of collected units meet the standards for a public bank. NMDP says units that do not qualify may still help through research. Anthony Nolan says it either disposes of them safely or uses them in research.

Public and private banks do different jobs. A public bank stores cord blood for any patient who needs it. A private bank stores it for one family, for a fee that insurance does not cover. The American College of Obstetricians and Gynecologists (ACOG) and the American Academy of Pediatrics both recommend public banking.

Donating cord blood is a one-time gift at birth. Joining a donor registry as an adult volunteer is a separate step. Registries list both. US guidelines from 2025 recommend searching for every donor type at the same time, rather than one after another.

Both kinds of donation help because matching depends on inherited HLA genes, and patients need donors from every background. The Jada Bascom Foundation does not enroll donors or test tissue types. It helps people find the official registry where they live.