Our blood has many special qualities. One is that a drop of blood from a rhesus monkey, attached to a drop of blood from a human being, will sometimes join together and sometimes not.
Since we know this, we divide people into groups with resuspositive and rhesus negative blood. A new blood group, in fact, in addition to the normal blood groups. Most people are rhesus positive, a small percentage of rhesus negative. The property is hereditary.
Now it has been found that when the father is positive and the mother is negative, the child may experience difficulties if it has inherited the positive factor from the father. Problems do not always occur, but it is wise to take this into account so that correct measures can be taken in plenty of time.
The circulatory system of mother and child are normally separated during pregnancy. Because the placenta is not permeable, it does not allow penetration of red blood cells of the child. Therefore no antibodies against the blood of her own child are produced by the mother.
If a child with rhesus positive blood develops in a mother with rhesus negative blood, a little blood from the child may possibly enter the mother's blood during birth. If complications occur during pregnancy, medical interventions are necessary, or in cases of miscarriage, the child's blood may also enter the mother's bloodstream.
Because the placenta is part of the afterbirth, during the rejection, rhesus positive blood cells of the child can pass through the permeable maternal blood vessels in the bloodstream of the mother with rhesus negative blood.
The child is not in danger because it is already born. In the mother's case, however, antibodies now develop, which attack the blood of the child, which does not fit with her own blood.
At a subsequent pregnancy, a small part of the mother's already present antibodies may end up in the child through the normally impenetrable placenta, because they are smaller than blood cells.
Such an event destroys a small amount of blood in the child. This is not dangerous. However, if the mother produces more and more antibodies, it can happen that too many of them enter the blood of the child so that it develops anemia. During the breakdown of blood a yellow chemical is released and the child therefore looks yellow immediately after birth, this is a mild jaundice.
In the worst case, a rhesus problem can cause brain damage to the child or even lead to death of the child.
To ensure that the mother stops producing antibodies with rhesus negative blood, and also to prevent as many problems as possible in subsequent pregnancies, she receives an anti-D immunoglobulin within about three days of birth.
During pregnancy you will be checked to see whether you are in the risk group, and you will receive one or more injections if this is indeed the case.