THE RHESUS FACTOR: HOW IT CAN AFFECT YOUR PREGNANCY
What is the Rh factor?
The Rh factor is a type of protein found on red blood cells. Most people have the Rh factor—they are Rh positive. Others do not have the Rh factor— they are Rh negative. A simple blood test can tell whether you are Rh positive or Rh negative.
When does the Rh factor cause problems?
The Rh factor causes problems when an Rh-negative person’s blood comes in contact with Rh-positive blood. If this happens, the person with Rh-negative blood may become sensitized. This means he or she produces antibodies that fight the Rh factor as if it were a harmful substance. Once formed, these antibodies do not go away. During pregnancy, the woman and fetus do not share blood systems. However, a small amount of blood from the fetus can cross the placenta into the woman’s system. When this happens, a small number of pregnant women with Rh-negative blood who carry an Rh-positive fetus will become sensitized and make antibodies against the Rh factor. These antibodies can attack and break down fetal Rh-positive red blood cells. This causes anemia, which can lead to a serious illness, brain damage, or even death of the fetus or newborn.
How can an Rh-negative woman become sensitized?
An Rh-negative woman can become sensitized if she is pregnant and carrying an Rh-positive baby. If the mother is Rh-negative, her baby can be Rh-positive only if the father is Rh-positive. If both the mother and the father are Rh-negative, there is no way the baby can be Rh-positive and there is no risk of the mother becoming sensitized. If the mother is Rh-positive and the father Rh-negative, sensitization does not occur.
When does sensitization occur?
In a first pregnancy with an Rh-positive fetus, the baby often is born before the woman’s body develops many antibodies, so there may be no serious problems. In a second pregnancy with an Rh-positive fetus, these antibodies are more likely to cause anemia in the fetus. In most cases, the condition becomes worse in later pregnancies.
When are women at risk of sensitization?
A woman can become sensitized at any time that Rh-positive blood mixes with her own. This can happen if an Rh-negative woman has ever:
- Had a miscarriage
- Had a termination of pregnancy
- Had an ectopic pregnancy
- Given blood
- Had an amniocentesis
- Had chorionic villus sampling
- Had bleeding during pregnancy
In each of these situations, small amounts of blood can mix with the mother's own, causing her to become sensitized.
Is there a test to see if sensitization has occurred?
A simple blood test can identify a woman’s blood type and Rh factor. Another blood test, called an antibody screen, can show if an Rh-negative woman has developed antibodies to Rh-positive blood.
How can anemia in the fetus of a sensitized woman be prevented?
Anemia can be prevented in the fetus if the Rh-negative woman has not yet made antibodies against the Rh factor. Rh immunoglobulin (RhIg) is a blood product that can prevent an Rh-negative mother from being sensitized. It prevents her body from responding to Rh-positive blood cells of the fetus. However, it is not helpful if the mother is already sensitized.
How is RhIg administered?
If an Rh-negative woman is given RhIg, it likely will be injected into a muscle of the arm or buttocks. The most common side effects are soreness where the drug was injected or a slight fever. Both side effects usually go away on their own.
When is RhIg administered?
If a woman with Rh-negative blood has not been sensitized, her health care provider may suggest that she receive RhIg around the 28th week of pregnancy to prevent sensitization for the rest of the pregnancy. This prevents problems in the small number of women who can become sensitized during the last 3 months of pregnancy. Sometimes, when a pregnancy has gone past the due date, another dose of RhIg is given.
How many treatments with RhIg are needed?
Shortly after birth, if the child has Rh-positive blood, the mother should be given another dose of RhIg. In almost all cases, this prevents the woman from making antibodies to the Rh-positive blood cells she may have received from her baby before and during delivery. The treatment is good only for the pregnancy for which it is given. Each pregnancy and delivery of an Rh-positive child requires a repeat dose of RhIg.
What happens if antibodies develop?
A mother who is Rh-sensitized will be monitored during pregnancy to see whether her baby is at risk. In some severe cases a baby with anemia may be born preterm, or may be given a blood transfusion while still in the mother's uterus. In less severe cases the baby may be born at the normal time. After the birth the baby may need a transfusion to replace its blood cells.