Cord blood testing provides immediate information about a newborn’s blood type and status. The small sample collected from the umbilical cord after birth allows medical staff to rapidly assess the baby’s potential for immune-related complications. Determining the baby’s blood type and checking for maternal antibodies is a time-sensitive process used to identify infants who may require immediate monitoring or intervention.
The Fundamentals of Cord Blood Typing
Cord blood typing focuses on the two most significant blood group systems: ABO and Rh. The ABO system classifies blood based on the presence of A and B antigens on the surface of red blood cells (Type A, Type B, Type AB, or Type O).
The Rh system is determined by the presence or absence of the RhD antigen, often called the Rh factor. If the RhD antigen is present, the blood type is positive; if absent, the type is negative. Combining these two systems results in the eight main blood types, such as O-positive or A-negative. A baby inherits these blood type genes from both parents.
Identifying these antigens is crucial because the immune system can recognize a foreign antigen and produce antibodies against it. The cord blood test quickly provides the newborn’s red blood cell profile. This information is compared with the mother’s known blood type and antibody status, recorded during prenatal care, to identify a potential mismatch.
Identifying Potential Blood Incompatibility Risks
Cord blood typing assesses the risk of Hemolytic Disease of the Newborn (HDN), which occurs when maternal antibodies attack the baby’s red blood cells. This immune reaction is triggered by a blood type difference between the mother and the baby. The mother’s immune system may become “sensitized” to the baby’s foreign red blood cell antigens, leading to the production of Immunoglobulin G (IgG) antibodies.
Rh incompatibility is the most severe form, occurring when an Rh-negative mother carries an Rh-positive baby. If the baby’s Rh-positive blood enters the mother’s circulation during pregnancy or birth, her body creates anti-D IgG antibodies. These IgG antibodies cross the placenta into the fetal bloodstream, attaching to the baby’s Rh-positive red blood cells and marking them for destruction (hemolysis).
ABO incompatibility is more common but milder, occurring most frequently when a Type O mother carries a Type A or Type B baby. Type O individuals naturally produce IgG antibodies against the A and B antigens. These maternal IgG antibodies can cross the placenta and destroy the baby’s red blood cells. The effect is less severe than Rh disease because A and B antigens are found on various other fetal tissues, which absorbs some of the antibodies.
Clinical Monitoring and Management Based on Results
Once an incompatibility risk is identified, specific monitoring protocols are implemented. A key test performed on the cord blood is the Direct Antiglobulin Test (DAT), which detects whether maternal antibodies have coated the baby’s red blood cells. A positive DAT confirms that immune-mediated hemolysis is occurring.
The destruction of red blood cells releases bilirubin, which can build up in the bloodstream and cause jaundice (hyperbilirubinemia). Infants with a positive DAT, particularly those with Rh incompatibility, are placed on an accelerated monitoring schedule for total serum bilirubin (TSB) levels. TSB levels are tracked against the baby’s age in hours to determine the risk of neurological damage.
The standard treatment for elevated bilirubin is intensive phototherapy, which uses special blue lights to change bilirubin into a form the baby can excrete more easily. If the TSB level is rapidly rising or approaching a dangerous threshold, a high-dose intravenous immunoglobulin (IVIG) infusion may be administered to slow the destruction of red blood cells. If TSB levels continue to climb despite aggressive phototherapy and IVIG, an exchange transfusion may be necessary. This procedure involves systematically removing small amounts of the baby’s blood and replacing it with compatible donor blood, which removes high bilirubin and antibody-coated red blood cells.