How Your Blood Type Can Affect Your Ability To Give Birth

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 is 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 is high, more of the red blood cells in the baby's blood will be destroyed. Destroying these red blood cells 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 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 where 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 who 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 two 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 or she 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.