The Rh factor blood group can cause couples a lot of grief. If a woman is Rh negative and her mate is Rh positive, and they make babies, there is a potential for compatibility problems between the mother and her developing child. This is one reason that it is advisable for couples to get blood tests before marriage, since these problems can be circumvented, if you have enough warning.
Here's how the problem is created.
Blood types are one of the kinds of marker systems that a mammalian body uses to identify its cells. This is important because mammals have a marvelous system called the immune system. The immune system is designed to identify cells and other things which are foreign to the body, and to destroy them. However, if the armies of the immune system (composed partially of an incredible group of proteins called antibodies) can't identify the cells which belong to the body, they will destroy those right along with the invaders.
So our blood cells have markers on their surfaces, and our immune systems have "learned" to leave cells marked like ours alone, and only to attack cells with different markers on them. This is why you couldn't give a person with Type A blood a transfusion of Type B blood the immune system would attack and destroy the B blood cells, which would not only make the transfusion worthless, but would create collateral problems because of the large amount of breakdown material created by the destruction of all those B cells.
The Rh factor is similar to the ABO blood type system, except that you aren't automatically sensitive to the wrong Rh blood type. The difference between Rh positive and Rh negative is that Rh positive cells have Rh markers on them, and Rh negative cells don't. So a person with Rh positive blood could receive Rh negative blood, and there would be no problem. However, if a person with Rh negative blood is exposed to Rh positive blood, the immune system would mobilize and begin to create armies of antibodies specialized to attack those Rh positive cells.
Now, we need to consider a little bit about gestation pregnancy, if you prefer. When a mother is gestating a baby, the mother's blood stream and the baby's blood stream do not mix. They are separated by the placenta. The mother passes all sorts of materials like carbohydrates, essential amino acids and vitamins, etc., across the placental barrier from her blood to the baby's, but their blood never mixes. Her immune system never "sees" the baby's blood cells.
So if an Rh negative mother is carrying an Rh positive baby, and her blood has never been exposed to Rh positive blood, there's no problem.
However, during delivery of the child, it is almost unavoidable that there is some mixing of the mother's and the baby's blood. It is very common for Rh negative mothers to become sensitized to Rh positive cells as a result of the delivery of an Rh positive child, though these days steps are taken to prevent this from happening. There is no damage to this first child.
(Of course, there are other ways she could become sensitized. The most probable is through a blood transfusion that isn't carefully enough matched. These days, hospitals try to be very careful about this.)
This is what sets up the problem. If our mother is now sensitized to Rh positive cells, her immune system is creating antibodies designed to attack Rh positive cells. Remember that I said that the mother's body passes all kinds of things across the placental barrier to the fetus? Well, one of the most important things she sends to her baby is antibodies those armies of the immune system. When a baby is born, its own immune system isn't yet activated, and it gets its protection from the antibodies passed on from the mother's blood.
However, if our Rh negative mother has been sensitized to Rh positive blood, her army of antibodies includes antibodies which will attack Rh positive cells including those of her Rh positive baby.
So the result is destruction of a lot of the baby's red blood cells. This leads to all kinds of problems, such as damage due to oxygen deficiency, since red blood cells are responsible for transporting oxygen to the tissues throughout the body, and jaundice due to the yellow-green breakdown products left over after red blood cells have been destroyed. Rh disease babies are born with a lot of problems, some of them pretty serious.
Modern medicine has made great advances toward preventing tragedies like Rh disease babies. The most important part of prevention is foreknowledge. If the mother and her doctor both know that she is liable to be in trouble with regard to Rh factor, they can take steps to prevent disasters. They can determine if she has been sensitized to Rh positive blood, and if she hasn't, they can prevent future exposure. When she delivers a child, there are drug treatments which will prevent her immune system from getting sensitized, so her future children won't be at risk.
If she is already sensitized, there are measures which can be taken to prevent or reduce the damage to a child she may carry.
There are far fewer Rh disease tragedies these days, thanks to medical progress.
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Updated 25 September 2004