Rh Factor And Pregnancy

March 5, 2009

When a woman finds out that she is pregnant, one of the first tests her medical provider will order is a blood test. Among other things, the doctor is looking for blood type and Rh (Rhesus) Factor. The Rh factor plays a very significant role in the baby's health, which makes this information important to have early in the pregnancy.

What Is Rh Factor And Why Is It So Important?

There are four major blood types in which people are categorized: A, B, AB, or O. These types are determined by the types of antigens on the blood. Antigens are proteins on the surface of the blood that cause the immune system to react or respond. Rhesus (Rh) factor refers to a specific antigen that is present on the surface of red blood cells. Most people, about 85 percent, have a positive Rh factor, the rest are considered to be Rh-negative.

There are potential problems that can arise from Rh factor incompatibility when an Rh-negative woman and an Rh-positive man conceive a baby. There is a likelihood the baby will have Rh-positive blood, inherited from the father. Usually there isn't a concern in a first pregnancy, unless there is an abnormality of some sort in which the baby's blood mingles with the mother's blood which can happen during delivery.

If the bloods mix, the mother's body recognizes the Rh-positive blood of the baby and will treat it as an invader by producing antibodies that work to destroy the foreign substance-in this case, the baby's blood. Other ways an Rh-negative woman who is pregnant may be exposed to the Rh protein that may cause an antibody reaction is through blood transfusions with Rh-positive blood, miscarriage or an ectopic (tubal) pregnancy.

What Can Happen To The Baby with Rh factor Problems?

Generally, with the first pregnancy, the difference in Rh factors between mother and baby are not troublesome. However, in future pregnancies there is a good chance that if she is carrying an Rh-positive baby, the antibodies in her Rh-negative blood will identify and attack the baby's blood as a foreign substance. This is particularly dangerous for the unborn baby because it can lead to swelling and rupture of the baby's red blood cells. The blood count can drop to perilously low levels and cause a condition known as haemolytic or Rh disease of the newborn.

There Is A Way To Prevent And Treat Rh Disease Of The Newborn

Today, unlike years ago when this was considered to be very serious, this problem can be treated with the administration of a series of two Rh immune-globulin shots during the woman's first pregnancy. Given at the 28th week initially with the second shot following within 72 hours after the birth of the baby, the Rh immune-globulin prevents the mother's blood from producing antibodies that would be dangerous to the new baby or complicate future pregnancies. If the situation gets out of control, which doesn't happen often, then exchange transfusions are needed to replace the baby's blood with blood that contains Rh-negative factor blood. This will stabilize the baby's red blood cell level and minimize damage to the baby.

Because Rh immune-globulin shots have been so very successful, exchange transfusions are not often needed in Rh-incompatible pregnancies today.

 

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