Umbilical cord is used in place of a bone marrow transplant in the treatment of blood disorders such as leukemia, with donations released for transplant through one registry, Netcord.org, passing 1,000,000 as of January 2013. Cord blood is used when the patient cannot find a matching bone marrow donor; this "extension" of the donor pool has driven the expansion of public banks. The umbilical cord in some mammals, including cows and sheep, contains two distinct umbilical veins. There is only one umbilical vein in the human umbilical cord. In some animals, the mother will gnaw through the cord, thus separating the placenta
Umbilical cord prolapse to congenital anomalies or prematurity, however. It is considered an emergency. The first sign of umbilical cord prolapse is usually a sudden decrease in fetal heart rate that is severe and does not immediately resolve. On a fetal heart tracing, this would usually look like moderate to severe variable decelerations. Occasionally, the cord can be seen or felt on vaginal examination, particularly with overt cord prolapse. Risk factors that are associated with umbilical cord prolapse tend to make it difficult for the fetus from appropriately engaging and filling the maternal pelvis or are related to abnormalities of the umbilical cord.