The Rh Factor

Scientists sometimes study Rhesus monkeys to learn more about the human body since there are certain similarities between the two species. During one study of the monkeys, a certain blood protein was discovered. This protein was found to be also present in the blood of most humans. However, approximately 15% of humans in the U.S. do not have the protein. The presence of the protein, or lack of it, is referred to as the Rh (for Rhesus) factor.If your blood does contain the protein, your blood is said to be Rh positive (Rh+). If your blood does not contain the protein, your blood is said to be Rh negative (Rh-).This Rh factor is connected to your blood type. For example, your blood may be AB+ which means that you have type AB blood with a positive Rh factor. Or, you might have O- blood which means that you have type O blood with a negative Rh factor.

Why Does It Matter During Pregnancy?

It is particularly important for an expectant mother to know her blood's Rh factor. Occasionally, a baby will inherit an Rh positive blood type from its father while the mother has an Rh negative blood type. If the mother is Rh-negative and her baby is Rh-positive, during pregnancy (and especially during labor and delivery) some of the fetus's Rh-positive red blood cells may get into the mother's bloodstream. Since these red blood cells are foreign to the mother's system, her body will try to fight them off by producing antibodies against them — a process called "sensitization."In a first pregnancy, there is less danger to an Rh-positive baby because the child is usually born before the mother produces substantial Rh antibodies. However, since the woman will continue to produce antibodies throughout her life, during her next pregnancy, maternal Rh antibodies can cross the placenta and reach the fetus. However, it is possible for an Rh-negative woman to be sensitized if she has previously had a miscarriage, an induced abortion, a blood transfusion, an ectopic pregnancy, or certain tests during pregnancy such as amniocentesis. The resulting disease, known as Rh disease, can destroy an unborn baby's blood cells, potentially resulting in newborns being born with jaundice (yellowing of the skin and eyes) and anemia. In some cases the disease can result in brain damage, heart failure, and even death of the baby. Today, however, doctors are able to detect and treat Rh disease in the fetus, so that more than 95 percent of babies with severe Rh disease survive.

Can Rh Disease Be Prevented?

A blood test will reveal whether or not a woman has Rh-negative blood. Every woman should be tested early in pregnancy, or prior to pregnancy, to find out. To prevent Rh disease, an Rh-negative woman should receive an injection of Rh immunoglobulin (RhIg) within 72 hours of delivering an Rh-positive baby. This prevents her body from reacting to the Rh-positive blood cells of the baby.RhIg prevents sensitization in more than 95 percent of Rh-negative women. However, studies show that about 2 percent of pregnant women become sensitized prior to delivery. For this reason, an RhIg injection is given around the 28th week of pregnancy as well.

Without RhIg Treatment

For women who have already developed antibodies, the Rh immunoglobulin treatment will not be effective. These women will be closely monitored throughout the pregnancy. Sometimes, the baby will become anemic and may either be given blood transfusions in the mother’s uterus, or delivered early before damage occurs. In other cases, the baby may have a normal delivery and then be given blood transfusions immediately afterward.

Remember

As always, becoming informed about your own health along with following your physician or midwife’s advice is the best way to protect your baby.