The Rh factor is a protein that can be present on the surface of red blood cells. Most people have the Rh factor: they are Rh-positive. Others do not have the Rh factor: they are Rh-negative.
The Rh factor is inherited. If the mother is Rh-negative & the father is Rh-positive, the fetus could be either Rh-positive or Rh-negative. If both the parents are Rh-negative, the baby also will be Rh-negative.
The Rh factor can cause problems if you are Rh-negative & your fetus is Rh-positive. This is called Rh incompatibility. These problems usually do not occur in the first pregnancy but can occur in later pregnancy.
When an Rh-negative mother's blood encounters blood from her Rh-positive fetus, it causes the Rh-negative mother to make antibodies against the Rh factor. These antibodies attack the Rh factor as if it were a harmful substance. a person with Rh-negative blood who makes Rh antibodies is called Rh sensitized.
During pregnancy, the women & fetus do not share a blood system. However, a small amount of blood from the fetus can cross the placenta into the women's system. This sometimes may happen during pregnancy & labor. It also can occur if an Rh-negative woman has had any of the following during pregnancy: Amniocentesis, Chorionic Villus Sampling (CVS), Bleeding during pregnancy, Manual rotation of the baby in a breech presentation before labor, and Blunt trauma to the abdomen during pregnancy.
During an Rh-negative women's first pregnancy with an Rh-positive fetus, serious problems usually do not occur because the baby often is born before the women's body develops many antibodies. If preventive treatment is not given during the first pregnancy & the woman later becomes pregnant with an Rh-positive fetus, the baby is at risk of Rh disease.
It is also possible to develop antibodies after an ectopic pregnancy or an induced abortion. If an Rh-negative woman becomes pregnant after one of these events, she does not receive treatment & the fetus is Rh-positive, the fetus may be at risk of Rh-related problems.
Problems during pregnancy can occur when Rh antibodies from an Rh-sensitized woman cross the placenta & attack the blood of an Rh-positive fetus. The Rh antibodies destroy some of the fetal red blood cells. This causes hemolytic anemia; where red blood cells are destroyed faster than the body can replace them... Red blood cells carry oxygen to all parts of the body. Without enough red blood cells, the fetus will not get enough oxygen. Hemolytic anemia can lead to serious illness > severe hemolytic anemia may even be fatal to the fetus.
A blood test called an antibody screen, can show if you have developed antibodies to Rh-positive blood & how many antibodies have been made. If you are Rh-negative & there is a possibility that your baby is Rh-positive, your health care provider may request this test during your first trimester & again during 28 weeks of pregnancy.
If you share Rh negative, you will be given a shot of Rh immunoglobulin (RhIg); it made from donated blood. When given to a non-sensitized Rh-negative person, it targets any Rh-positive cells in the bloodstream & prevents the production of Rh antibodies. When given to an Rh-negative woman who has not yet made antibodies against the Rh factor, RhIg can prevent fetal hemolytic anemia in later pregnancy.
RhIg is not helpful if you are already Rh sensitized.
RhIg is given to Rh-negative women in the following situation: At around the 28th week of pregnancy to prevent Rh sensitization for the rest of the pregnancy. Within 72 hours after the delivery of an Rh-positive infant. After a miscarriage, abortion, or ectopic pregnancy. After amniocentesis or chorionic villus samples.
If you are Rh sensitized, you will be monitored during pregnancy to check the condition of your fetus. If a test shows that your baby has severe anemia, it may be necessary to deliver your baby early (before 37 weeks of pregnancy) or give a blood transfusion while your baby is still in your uterus (through the umbilical cord). If the anemia is mild, your baby will be delivered at the normal time. After delivery, your baby may need a transfusion to replace the blood cells.