Complications: Rh Incompatibility and Isoimmunization

All of us have a specific blood group, such as A, B, AB, and O. In addition to the blood group, we have a blood type, which is either Rh-positive, or Rh-negative. Rh is a term used to describe a specific surface antigen that are found on our red blood cells. People that have Rh-positive blood (such as A-positive) have the antigen on their red blood cells. Those that have Rh-negative blood (such as O-negative) do not have the antigen on their red blood cells.

When you to go your first prenatal appointment with your obstetrician or midwife, you will have blood drawn. The blood will be sent to a laboratory to see what your blood group, and type is. The lab will also check to see if your body has formed any antibodies.

If Rh-positive blood enters the bloodstream of a person with Rh-negative blood, the immune system will recognize the Rh-positive blood as a foreign substance and begin making antibodies to fight against it. This is referred to as Rh incompatibility, or Rh disease.

First-time pregnancies are usually unaffected by Rh incompatibility. However, if you have had a miscarriage or an abortion, or if you were given Rh-positive blood in the past, your body may have produced antibodies which could affect the health of you and the baby. If the father of the baby is Rh-negative, the baby will be Rh-negative, so there is no need to perform testing to determine baby’s blood type.

Risks associated with Rh incompatibility

This may happen before the baby is born if a small amount of baby’s blood crosses through the placenta into the mother’s circulating blood. It can also happen during the delivery of her baby.

When this happens, the mother’s immune system responds to the baby’s blood in the same way that it would react to any abnormal substance by forming antibodies to fight against it. These antibodies remain in the mother’s body. When antibodies are present in the mother’s blood, it is called Rh-D isoimmunization.

If the mother becomes pregnant again with another Rh-positive baby, the antibodies that are already present in her immune system may travel on top of her red blood cells across the placenta into the baby’s bloodstream. When this happens, the antibodies can destroy red blood cells in the baby’s body. How many red blood cells that are destroyed depends upon how many antibodies there are in the mother’s bloodstream. If the number of antibodies are low, the baby’s body can make new red blood cells to replace the ones that were destroyed. If the number of antibodies in the mother’s bloodstream are high, more of the red blood cells in the baby’s blood will be destroyed. Destroying these red blood will cause the baby to be anemic. The more red blood cells that are destroyed, the worse the anemia will be.

The destruction of baby’s red blood cells can cause a condition called Hydrops Fetalis (Hemolytic Disease of the Newborn), or can lead to kernicterus, also known as newborn jaundice.

What happens after the test?

If you have Rh-negative blood and your immune system has not formed any antibodies, you will receive a medication (an injection) called anti-D immune globulin (RhoGam) when you are in your 28th week of pregnancy. This medicine works to prevent your body from making the antibodies that could destroy your baby’s red blood cells. After your baby is born, blood from the umbilical cord will be tested to find out what type of blood your baby has. If baby has Rh-positive blood, you will receive another dose of anti-D immune globulin before you are discharged from the hospital. If your baby’s blood type is Rh-negative, you do not need another dose. The dose of medication is given to you after you deliver to prevent your body from making antibodies in case you become pregnant again with a Rh-positive baby.

In situations in which a pregnant woman already has antibodies, a test may be necessary to check the blood type of her unborn baby. There is a blood test (cell-free DNA) that can be done after her 8th week of pregnancy; however, the test is not available everywhere, and may not be covered by the mother’s insurance.

In situations where the mother’s antibody level is very high, an amniocentesis may be performed after the 15th week of pregnancy to determine baby’s blood type. An amniocentesis is only performed when the mother’s blood contains very high levels of antibodies because there is a risk of causing more blood to mix between mom and baby.

If the test results show that the mother is carrying a baby that is Rh-positive, she should have blood work (titers) drawn once every month during her pregnancy to see if the number of antibodies is increasing. If the titers begin to rise, the test should be done every 2 weeks. This will alert her physician when the antibodies in her bloodstream have climbed to a level that could cause serious harm to her baby.

If the antibodies in the mother’s bloodstream climb to a level that could cause serious harm to her baby, she should have a special test (Doppler velocimetry) done. This measures the amount of blood that flows through the middle cerebral artery in baby’s brain. If the blood flow is less than normal, the baby may have severe anemia. This test may be done every one to two weeks.

If the Doppler test shows that the baby may have severe anemia, and the mother is between her 18th and 35th week of pregnancy, a test may be done to check the amount of hemoglobin in the baby’s bloodstream. If the test shows that the amount of hemoglobin is very low, a blood transfusion may be given to the baby while he is still inside the uterus (intrauterine fetal transfusion).

If a woman becomes pregnant again after a pregnancy that was complicated by Rh(D)-isoimmunization, she will develop complications earlier in the pregnancy, and the complications will be more severe.

Preventing Rh incompatibility for future pregnancies

The only 100% accurate way to be sure there is no Rh incompatibility issue is for the mother to undergo in vitro fertilization, where the blood type of each embryo will be checked, and only the embryos with a Rh-negative blood type would be implanted. A surrogate sperm donor with a Rh-negative blood type may also be used, or a woman who acts as a surrogate (carries a baby for another woman) may be considered.

However, there are some things you can do that may help prevent Rh-D isoimmunization. If a woman has a Rh-negative blood type, she should receive an anti-D immune globulin injection (RhoGam) during each pregnancy that she has. She should also receive the injection if she has a miscarriage, ectopic pregnancy, or abortion.

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  1. Moise, K. (2016). Overvew of Rhesus D alloimmunization in pregnancy. UpToDate. Retrieved from http://www.uptodate.com/contents/overview-of-rhesus-d-alloimmunization-in-pregnancy