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Rhesus factor disease
Blood groups are all based on the presence or absence of special proteins on the surface of red blood cells. The rhesus factor protein is the next most important one after the A and B proteins. The gene that makes a person rhesus positive is present in 85% of the population.
The importance of blood groups is that someone without a particular blood group protein who is given blood (by transfusion) containing that protein, will develop antibodies to it, and effectively be allergic to it. For instance, people with blood group A do not have the B protein, and giving such a person blood from group B or AB (where both A and B proteins are present) will cause a serious reaction that may lead to death. Someone with blood group O has neither protein, so can only receive blood from another group O donor, but can give blood to any group.
Problems from rhesus factor usually occur only in pregnancy. If a baby is rhesus positive but the mother is rhesus negative, then the mother could become sensitive to the baby’s blood. The mother’s blood does not usually come into contact with the baby’s until labour, so this difference is unlikely to cause serious harm in the first pregnancy.
Unfortunately, during that first labour, the mother’s body produces antibodies to the rhesus protein. In later pregnancies where the baby is also rhesus positive, the levels of these antibodies in the mother’s blood rise rapidly. They soon reach a point at which they are able to destroy the red blood cells of the baby.
