Rh Factor and Pregnancy

The Rh factor is the type of protein on red blood cells. Most people have the Rh factor and are thus labeled Rh positive. Others do not have the Rh factor and they are Rh negative. If a woman who is Rh negative and a man who is Rh positive conceive a baby, there is the potential for a baby to have a health problem.

During pregnancy, you will have a blood test to find out your blood type.  People with different blood types have proteins specific to that blood type on the surfaces of their red blood cells. There are four blood types - A, B, AB, and O.

Each of the four blood types is additionally classified according to the presence of another protein on the surface of red blood cells that indicates the Rh factor. If you carry this protein, you are Rh positive. If you do not carry the protein, you are Rh negative.

The Rh factor causes problems when an Rh-negative person's blood comes in contact with Rh-positive blood. 

The following has been adapted from the websites listed at the bottom of the page.

More than 85% of people in the world are Rh positive. But if a woman who is Rh negative and a man who is Rh positive conceive a baby, there is the potential for a baby to have a health problem. The baby growing inside the Rh-negative mother may have Rh-positive blood, inherited from the father. Approximately half of the children born to an Rh-negative mother and Rh-positive father will be Rh positive.

Rh incompatibility usually is not a problem if it is the mother's first pregnancy because, unless there is some sort of abnormality, the fetus's blood does not normally enter the mother's circulatory system during the course of the pregnancy.

However, during delivery, the mother's and baby's blood can intermingle. If this happens, the mother's body recognizes the Rh protein as a foreign substance and can begin producing antibodies against the Rh proteins introduced into her blood.  Other ways Rh-negative pregnant women can be exposed to the Rh protein that might cause antibody production include blood transfusions with Rh-positive blood, miscarriage, and ectopic pregnancy.

Rh antibodies are normally harmless until the mother's second or later pregnancies. If she is ever carrying another Rh-positive child, her Rh antibodies will recognize the Rh proteins on the surface of the baby's blood cells as foreign, and pass into the baby's bloodstream and attack those cells. A baby's blood count can get dangerously low when this condition, known as hemolytic or Rh disease of the newborn, occurs.

How Is Rh Disease of the Newborn Prevented and Treated?

In generations past, Rh incompatibility was a very serious problem. Today, if a woman  has Rh-negative blood her health care provider may suggest that she receive Rh immune-globulin shots around the 28th week of pregnancy to prevent sensitization for the rest of the pregnancy. Shortly after birth, if the child has Rh-positive blood, the mother is again given Rh immune-globulin shots.  This treatment prevents the woman from making antibodies to the Rh-positive cells she may have received from her fetus before and during delivery. A dose of Rh immune-globulin may also be given if a woman has a miscarriage, an amniocentesis, or any bleeding during pregnancy.

If a doctor determines that a woman has already developed Rh antibodies, then the pregnancy will be closely monitored to make sure that those levels are not too high.

To protect against Rh factor problems, all pregnant women should have a blood test done at an early stage of pregnancy.  Make sure to discuss the Rh factor, and any other concerns you may have regarding your pregnancy, with your health care provider.

What Can Happen if Rh Disease Is Not Prevented?

Rh incompatibility rarely causes complications in a first pregnancy and does not affect the health of the mother. But Rh antibodies that develop during subsequent pregnancies can be potentially dangerous to mother and child. Rh disease can result in severe anemia, jaundice, brain damage, and heart failure in a newborn. In extreme cases, it can cause the death of the fetus because too many red blood cells have been depleted.

If you're not sure what your Rh factor is and think you are pregnant, it is important to start regular prenatal care as soon as possible.