Rh Factor and Your Pregnancy

If  you are pregnant, you should know both your blood type and your Rh factor. Knowing your blood type is important for anyone, but it is especially important when you are deciding to have children and while you are pregnant. Knowing your Rh factor is even more important during your pregnancy.

There are four types of blood in humans: type O, type A, Type B, and Type AB. Types A, B, and AB have certain proteins on the surfaces of their red blood cells, with type A having one kind or protein, type B another, and type AB having both. Type O blood does not have either of these proteins.  The most common blood type is type O, with about 45% of the population, followed by type A with 40%, and type B with 10%. The rarest blood type is type AB with only about 5% of the population. (Some people have blood that doesn’t fall into these groups, but that is an exceedingly rare case.)

There is also another blood protein called the Rh factor that is very important during pregnancy. Some people have Rh factor, and some people don’t. About 15% of people do not have Rh factor and are therefore Rh negative. A person’s blood type can thus be type O positive for someone with type O blood and Rh factor or type B negative for someone with type B blood and no Rh factor.

Both blood type and the presence of Rh factor are inherited from your parents, just as your baby has inherited blood type and the presence of Rh factor from you and your partner.

Rh Incompatibility

If you are Rh negative and your partner is Rh positive, and if your baby inherits the Rh gene, you may experience a problem called Rh incompatibility. Incompatibility does not occur if you are your partner have different blood types, such as O or A. It only occurs if you are Rh negative and your partner is Rh positive.  If you both are Rh positive, of if you are Rh positive and your partner is Rh negative, there is no problem.

However, if you are Rh negative and your unborn baby is Rh positive, you are Rh incompatible.

You and your baby normally do not share blood during the pregnancy. Your bloodstream and your baby’s bloodstream are separated by the placenta. However, sometimes during pregnancy, a little bit of the blood of the baby crosses the placenta into the bloodstream of the mother and can sensitize her immune system. This blood crossover and Rh sensitization can occur due to amniocentesis or chorionic villus sampling, if there is bleeding during pregnancy, or if there has been any trauma to the abdomen during pregnancy. If this happens, an Rh negative mother’s blood will then react to the Rh protein in her baby’s blood by forming antibodies to destroy the Rh positive blood.

These antibodies are formed during a first pregnancy, but that first baby will usually not have any problems.  During later pregnancies with Rh positive babies, the mother makes antibodies in greater amounts which is why future pregnancies are at risk.

In future pregnancies, antibodies from the mother cross the placenta and attack the blood cells in the baby. This causes a serious form of anemia because the baby cannot replace the blood cells as fast as they are being destroyed. In some cases, the baby can die before birth or shortly afterward from anemia or be born with jaundice. This condition is called hemolytic disease of the fetus and newborn.

Rh incompatibility can occur even if the pregnancy is not carried to term. Antibodies can form in an Rh negative woman who has had a miscarriage, an ectopic pregnancy, or an abortion.

Problems From Rh Incompatibility Can Be Prevented

There is a treatment for Rh compatibility that basically prevents you from making antibodies against the Rh factor. This is why your midwife or obstetrician will test a sample of blood at your earliest prenatal visit to find out if you are Rh negative.

If you are Rh negative, your healthcare provider may also test your blood to see if you already have antibodies to Rh protein, and if so, how many. This test is called an antibody screen.

There is a medication that can prevent the formation of antibodies against Rh factor in the mother. It is called Rh immunoglobulin or RhIg (brand name, RhoGAM). RhIg is given by injection and needs to be administered around the 28th week of pregnancy. If your baby is Rh positive, you will be given another dose within 72 hours of delivery.

Because of RhIg, very few babies have problems with Rh incompatibility. At one time, Rh incompatibility was a serious problem that affected up to 10% of births and that led to miscarriages and stillbirths. Having a treatment that can prevent problems from Rh incompatibility has made pregnancy and childbirth safer.

Valerie DeBenedette
Valerie DeBenedette is an experienced health and medical writer who lives about an hour north of New York City with a dog that is smaller than her cat. Her work has appeared in magazines, newspapers, newsletters, and on websites. She is a member of the National Association of Science Writers.

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