Rh Factor

From LoveToKnow Pregnancy

Rh Factor and Pregnancy

You might have heard about Rh Factor as something you’ll be tested for during pregnancy. Or perhaps you know someone who had trouble with Rh incompatibility during a pregnancy.

A, B, AB, and O are the four blood types. Rh is another part of blood typing. Rh factor is a protein which appears on red blood cells in about 85% of people. When people talk about blood being "positive" or "negative" (as in AB-positive or O-negative), they’re talking about the Rh factor.

The Rh factor is important in pregnancy because if a woman is Rh-negative and her baby is Rh-positive, the baby’s life could be in danger. When an Rh-negative person’s immune system detects Rh-positive blood, it makes antibodies that attack the blood cells just as if they were dangerous bacteria. These antibodies can cross the placenta and destroy the baby’s red blood cells.

Who Is at Risk?

A baby's Rh type is inherited from the parents. A pregnant woman is at risk of problems with Rh sensitization if she is Rh-negative and the father of her baby is Rh-positive.

Rh Sensitization

Most Rh-negative women won’t ever have a problem with Rh factor during pregnancy. The baby's blood doesn't normally mix with the mother's during development, so the mother never makes any antibodies. But, sometimes the baby's blood does get into the mother's system. This happens most commonly during labor, but it can also happen during amniocentesis or other procedures, if the mother is injured, or even during a seemingly normal pregnancy.

The first time the mother’s body encounters Rh-positive cells, it reacts slowly. By the time her immune system produces antibodies, it’s usually too late to hurt the baby. But, her system is now sensitized to Rh factor. Next time it comes into contact with Rh-positive blood, it can start making antibodies within hours. So if the woman becomes pregnant with another Rh-positive baby, this new baby is at risk.

Rh sensitization is permanent. Once a women's immune system becomes sensitized, each new pregnancy with an Rh-positive partner must be closely monitored for problems.

Rh Disease

When a baby is affected by Rh antibodies from the mother's blood, it's called Rh Disease, hemolytic disease, or hemolytic anemia. Hemolysis is the destruction of red blood cells. Anemia means that the baby does not have the ideal number of red blood cells to carry oxygen throughout the body.

As red blood cells are destroyed by the mother's Rh antibodies, the baby becomes anemic. In mild cases, the anemia does not harm the baby. In the most severe cases, the baby develops dangerous swelling and anemia, a condition called hydrops fetalis.

Treatment focuses on keeping the baby as safe as possible. Sometimes, the pregnancy can be continued with careful monitoring. Sometimes early delivery or c-section is needed. In severe cases, the unborn baby may need a blood transfusion, while still in your womb, to give him/her enough red blood cells to survive. In the worst cases, the baby does not survive.

Rh Testing

You should be tested for your Rh type early in your pregnancy, or even before you get pregnant. If you are Rh-negative, you’ll be tested to see if you have been sensitized to Rh-positive blood. Occasionally, even someone who has never been pregnant will have been sensitized.

If you have been sensitized, or if you become sensitized at any point during the pregnancy, you will need close monitoring to make sure the baby is not being harmed. Tests might include amniocentesis, a special ultrasound to look at the baby’s blood vessels, or even sampling of the fetal blood.

If you have not been sensitized, you should be tested again at about 28 weeks of pregnancy.

Rh Immune Globulin

If your test for sensitization is still negative at 28 weeks, you will probably be offered a shot of Rh immune globulin, also called Rhogam. Rh immune globulin is very effective at preventing sensitization to Rh factor during the rest of the pregnancy.

If the baby turns out to be Rh-positive, you can expect to receive one more shot of Rh immune globulin after labor.

Rh immune globulin is also given in other circumstances related to pregnancy, when an Rh-negative woman might be exposed to Rh-positive blood. These include miscarriage, elective abortion, and ectopic pregnancy.

Women with religious concerns about blood transfusions will want to be aware that Rh immune globulin is a blood product. Thanks to careful screening, the risk of contracting a disease from Rh immune globulin is extremely small.