Rh Factor

The facts on Rh incompatibility

Early in your pregnancy, your obstetrician will order blood type tests. You may think little of these and not really know what they're for, but one of the things your doctor is looking for is your blood's so-called rhesus or Rh factor. Your rhesus factor simply refers to the presence or absence of a unique protein found in red blood cells, and you're either Rh positive or Rh negative. The only time your Rh factor may affect your health is when you're pregnant and an Rh incompatibility exists between you and your partner.


When Is a Pregnant Woman at Risk?

Rh incompatibility occurs when an Rh negative woman is impregnated by an Rh positive man, which can result in an Rh positive fetus. If the fetus is Rh positive and its mother is Rh negative, there is a risk of a potentially serious adverse reaction if any of the fetus' blood enters the mother's bloodstream. Should this occur, the mother's body will produce antigens against the Rh positive blood, and her immune system will mistake the fetus for a harmful intruder (a condition known as "Rh disease"). The end result is that the fetus' red blood cells can be damaged or destroyed, resulting in possible anemia, hemophilia, brain damage or even death. Once a woman has been sensitized to an Rh-incompatible fetus, her body will continue to produce antibodies for the rest of her life, putting subsequent pregnancies at even greater risk.

If you are Rh positive, you have no reason to worry, as this precondition makes it impossible for Rh disease to develop and your baby is not at risk. Similarly, if you and your partner are both Rh negative, any children you conceive will also be Rh negative with no risk of Rh incompatibility.

Addressing Rh Incompatibility

Early blood tests can detect Rh incompatibility, and if it exists, the mother can be given an immunoglobin injection known as RhoGAM. This injection will inhibit the immune system of the mother from producing the antibodies which will attack Rh positive red blood cells, thus minimizing the possibility of harm to the fetus. Rh negative women are often given a routine, preventative RhoGAM shot at 28 weeks of pregnancy. It is also vital that they receive an injection within 72 hours of any event that may have caused maternal and fetal blood to mix, including miscarriage, amniocentesis and childbirth.

Reactions to the RhoGAM injection are relatively rare and comparatively mild. The vast majority of women experience no more than some soreness or irritation at the injection site and a slight fever which goes away fairly quickly. However, when an Rh incompatibility exists, you will need careful prenatal care to ensure that your baby doesn't develop anemia or any of the more serious complications associated with Rh disease.