What Does My Child's Blood Type Depend On?
Although it seems surprising, blood type isn’t genetically determined at birth simply by taking into account the contributions of both parents. To accurately identify it, a doctor or nurse must take a blood sample from the child and perform the subsequent analysis.
Blood type is classified according to the presence or absence of antigens on the surface of red blood cells. The presence or absence of certain antigens is what determines if the child belongs to one group instead of another.
There are three types of antigens (A, B, and AB) that make up four different blood groups. Additionally, the absence of antigens on the surface of red blood cells typically identifies group O.
Therefore, two possible expressions of this gene compose our genotype, which results in the following combinations: AA, AB, AB, AO, BO, and OO. On the one hand, genes A and B are dominant (expressed), and on the other hand, gene O is recessive (expressed only in the presence of a second gene O).
2 large groups: ABO and Rhesus
There are more than 20 different types of possible incompatibilities that are formed by two large groups: the ABO system and the Rh factor. We’ll now describe each one.
The incompatibility, in this case, is usually milder and may appear in the first pregnancy. There are three different antigens: A, B, and O, which will determine the groups. They can be A, B, AB, or O.
People who have antigen A on the surface of their red blood cells create antibodies — molecules that attack — against B antigens. Those in group B do the reverse and have antibodies against group A.
Individuals in group O have neither A nor B antigens on their surface, and therefore, can make antibodies against A and B. Finally, those of group AB won’t produce antibodies against either group since they have the two antigens on their surface.
For example, people who have their cell wall formed by type A antigens will be able to make antibodies against those of type B. It wouldn’t make sense for them to create antibodies against A because they would be attacking themselves.
The Rhesus factor also determines your blood type. It indicates the presence or absence of a particular antigen in red blood cells. The Rhesus factor can be positive (Rh +) or negative (Rh -).
The most frequent problems of maternal-fetal incompatibility (and therefore mother-father) depend mainly on the Rh factor.
When both parents have a negative Rh factor, regardless of their blood group, the child will necessarily have a blood group with a negative Rh. In other cases, the child may have a blood group with a Rhesus + or -.
“There are three types of antigens (A, B, and AB) that make up four different blood groups; Group O is characterized by the absence of antigens on the surface of red blood cells.”
How is the blood group inherited?
Blood groups are inherited by the parents: half of the mother and half of the father.
A single gene controls the ABO system group information, where A and B are dominant, just as the brown gene dominates over the blonde or the dark eyes gene over the light ones. In this case, either A or B dominate over O. Thus, people with either AO or AA will be in the A group.
Incompatibility between groups
When there’s incompatibility, the baby’s cells are attacked by the mother’s antibodies. These are destroyed and can lead to anemia and hyperbilirubinemia. It may be less severe in cases of incompatibility by the ABO system in comparison to the Rh factor, which could be serious.
Incompatibility between groups is rare, although it may happen in the following cases:
- Mother with group A, B, or AB positive: it’s not necessary to know the father’s group.
- Mother with group O positive: it’s advisable for the father to get a blood test because if he is A, B, or AB, the child could have jaundice at birth due to ABO incompatibility. This isn’t a serious pathology, but knowing the father’s group speeds up the diagnosis.
- If the group is the same in both parents, there are no problems for the baby.
You should definitely bear in mind that testing to discover the blood type is very important during pregnancy. This serves to find incompatibilities in the couple that may cause problems to the fetus. Therefore, prevention is of vital importance.