Rh Factor And Pregnancy

When the pregnancy test comes back positive, frequently the next step for a woman is to have blood work done. Blood tests help determine many things, among them the Rh factor in the blood. Each person's blood is categorized in one of four major groups: A, B, AB, or O. The types of antigens in the blood cells determine the blood type. Antigens are proteins that occur on the blood's surface and trigger a response from the immune system.

What Is Rh Factor?

Rhesus (Rh) factor refers to a specific antigen in the blood. If the blood does not have the Rh antigen, then the blood is Rh-negative. Conversely, if there is the Rh antigen in the blood, then it is Rh-positive. Most people are Rh-positive. However, if a woman who is Rh-negative conceives a baby with a man who is Rh-positive, the baby may inherit the father's antigens and be Rh-positive as well. About 50 percent of babies born to this combination of parents are born with Rh-positive blood. Problems can arise when the fetus's blood has the Rh factor (positive) and the mother does not (negative.)

What Happens If There Is Rh Incompatibility?

Rh incompatibility is not usually a problem in a first pregnancy unless there is some abnormality in the pregnancy. This is because the baby's blood does not normally enter the mother's circulatory system during the pregnancy. However, it is possible for the baby's blood to mingle with the mother's blood during delivery. Should this happen, the mother's body may react as if it is allergic to the baby by making antibodies to the Rh antigens in the baby's blood. The mother's blood has become sensitized and her antibodies can cross over the placenta to attack the baby's blood.

The result of the sensitization is a breakdown of the baby's red blood cells and subsequently, anemia. The condition is called hemolytic disease or hemolytic anemia. If untreated, the results can be very serious, including brain damage, serious illness, or even death of the baby. Any time the baby's blood mixes with the mother's blood, sensitization can occur. If a woman has had a miscarriage, induced abortion, or menstrual extraction, a tubal pregnancy, chorionic villus sampling or a blood transfusion, she may be sensitized to Rh-positive blood.

What Can Be Done To Deal With The Problem?

In the past, Rh incompatibility was a very serious and often life-threatening problem. However, today a blood test can provide the information as to blood type and Rh factor. Antibody screening is another method of determining if an Rh-negative woman has produced antibodies to Rh-positive blood. A woman with a predisposition to developing Rh incompatibility can receive a series of two Rh immune-globulin shots during her first pregnancy. The first shot is given at around the 28-week mark and the second within 72 hours of giving birth. These shots act like a vaccine, preventing the mother's body from producing Rh antibodies that could seriously harm her baby. They also act as a deterrent to complications in any future pregnancies.

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