Cord blood is the blood remaining in the umbilical cord and placenta after birth, and it is entirely the infant’s own blood. It possesses the baby’s unique blood type and genetic characteristics. Collecting a sample of this blood is a standard procedure that provides healthcare providers with important information about the newborn’s health. The blood type determined from this sample is the one the child will carry throughout their life, which has immediate and long-term implications for the child’s care.
The Identity of Cord Blood
Cord blood is identical to the blood flowing through the newborn’s veins after delivery. This blood contains all the typical components found in whole blood, including red blood cells, white blood cells, platelets, and plasma. The red blood cells in this sample already express the specific antigens, or protein markers, that determine the baby’s ABO and Rh blood type. Although the umbilical cord connects the baby and the placenta for nutrient exchange, the baby’s blood and the mother’s blood normally remain in separate circulatory systems and do not mix. Thus, the blood type found in the cord is solely the baby’s genetic expression and may differ from the mother’s type.
Genetic Inheritance of Blood Types
A baby’s blood type is a trait inherited from both parents, dictated by specific genes that control the presence of antigens on the surface of red blood cells. The ABO system involves three possible gene versions, known as alleles: A, B, and O, with A and B being co-dominant and O being recessive. A baby inherits one allele from each parent, which means a child’s blood type may not be the same as either parent, though it is always a predictable combination of their genes.
For example, two parents who both have Type A blood might each carry a recessive O allele, allowing them to have a child with Type O blood. Conversely, if one parent is Type A and the other is Type B, their child could potentially be Type A, Type B, Type AB, or Type O, depending on the specific alleles inherited. The ABO blood group is fully formed and detectable at birth.
The Rh factor, which determines if a blood type is positive or negative, is governed by a separate set of genes, following a similar pattern of inheritance. The Rh-positive gene is dominant, meaning a baby only needs to inherit one positive gene from either parent to have a positive blood type. If both parents are Rh-negative, they must both carry only negative genes, ensuring their baby will also be Rh-negative. The combination of the ABO group and the Rh factor results in one of the eight major blood types, all of which are established in the cord blood.
Practical Applications of Cord Blood Typing
One of the most important uses of cord blood typing is to identify potential maternal-fetal incompatibility, particularly with the Rh factor. If a mother is Rh-negative and the baby is Rh-positive, the mother’s immune system could be exposed to the baby’s blood, causing her body to produce antibodies against the Rh-positive red blood cells. This Rh incompatibility can lead to Hemolytic Disease of the Newborn (HDN) in future pregnancies. Knowing the baby’s Rh status from the cord blood allows doctors to determine if the Rh-negative mother needs an injection of RhoGAM, which prevents this immune reaction. Cord blood testing also helps diagnose HDN if the baby is presenting with symptoms like jaundice.
Determining the blood type is also a necessary step for parents who choose to bank or donate their baby’s cord blood. Cord blood is a rich source of hematopoietic stem cells, which can be used in transplants to treat over 80 diseases, including various cancers and blood disorders. The blood type is a part of the overall genetic profile recorded for the sample, and this information is essential for matching the stem cells with a patient in need of a transplant.