Cord blood is the blood remaining in the placenta and umbilical cord after a baby is born. This sample contains a rich supply of blood cells and stem cells. As an extension of the baby’s own circulatory system, this collected blood is often tested to provide immediate and long-term health information. Because the identity of this blood is sometimes confusing for new parents, a small sample is routinely collected and analyzed in the hospital.
Cord Blood is the Baby’s Blood Type
The blood collected from the umbilical cord is genetically and physically the baby’s own blood, separate from the mother’s circulation. The placenta acts as a sophisticated filter and exchange surface, preventing the mother’s blood from mixing directly with the baby’s blood. This mechanism ensures that the cord blood reflects the newborn’s individual genetic profile, including the inherited blood type. The blood type, determined by antigens on the surface of red blood cells, is fixed at conception, just like other genetic traits.
This sample is a direct representation of the baby’s red blood cells, carrying the specific ABO group and Rh factor. The blood type is a combination of genetic material from both parents but is not influenced by the mother’s type. Cord blood analysis provides accurate information regarding the newborn’s blood characteristics, making it the preferred sample for immediate typing and other neonatal tests.
Determining Blood Type in Newborns
Healthcare providers often test cord blood to determine the newborn’s ABO group and Rh factor. The Rh factor (positive or negative) is always immediately checked if the mother is Rh-negative. Knowing the baby’s Rh status determines whether the mother needs an injection of Rho(D) immune globulin to prevent her immune system from creating antibodies that could affect future pregnancies. The ABO type (A, B, AB, or O) is also assessed, but results can sometimes be complicated by the presence of maternal antibodies.
Infants do not fully produce their own antibodies at birth; any antibodies present typically crossed the placenta from the mother. These maternal antibodies can interfere with standard ABO grouping tests, particularly the “reverse type” test. For this reason, an infant’s ABO group is often confirmed later in life, usually after six months, when their own antibody production has matured. However, the immediate cord blood test reliably identifies the presence of blood group antigens on the baby’s red cells.
Why Maternal Blood Can Affect Testing
The process of collecting the cord blood sample carries a small risk of contamination with maternal blood. This can occur during collection if the umbilical cord is not properly cleansed or if the mother’s blood is inadvertently introduced into the collection bag. Even a small amount of maternal blood can temporarily skew the results of a blood type test, as the test would be reading a mixed sample.
This risk is a concern, especially in facilities that collect cord blood for banking. To mitigate this, strict protocols are followed during collection, and laboratories perform checks to ensure the sample is not contaminated. If a sample is suspected to contain a mixture of maternal and fetal blood, it may be rejected for banking or require further testing to isolate the pure neonatal blood type.
Applications of Cord Blood Typing
Knowing the cord blood type is immediately relevant for assessing the newborn’s health and planning immediate treatments. A primary application is screening for Hemolytic Disease of the Newborn (HDN), which occurs when the mother’s immune system creates antibodies against the baby’s red blood cells. HDN is most commonly associated with Rh factor incompatibility, but can also occur with ABO incompatibility, particularly if the mother has type O blood. Cord blood testing confirms whether the baby’s red cells are being coated by these maternal antibodies, which can lead to rapid red blood cell destruction.
The cord blood type is also necessary for preparing for potential neonatal transfusions. If a newborn requires a transfusion shortly after birth due to severe jaundice or anemia, the correct ABO and Rh matching is immediately available from the analysis. For parents who choose to bank their child’s cord blood for future therapeutic use, the blood type is recorded for matching purposes. The stem cells found in cord blood are used in transplants to treat various malignant or genetic blood disorders.