What Causes Rh Incompatibility?

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  • Last Modified Date: 02 November 2019
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Rh incompatibility is a very rare, yet severe condition. It is completely preventable, given the ease at which a mother’s blood can be tested. Essentially, the Rh factor is a specific protein that exists on blood cells of people who have positive blood. If one lacks this protein, a perfectly healthy variant, one is considered to have negative blood.

Rh incompatibility only occurs in pregnant women with a negative blood type. She must further conceive a child who has a positive blood type. This means the birth father must have positive blood. During a woman’s first pregnancy, Rh incompatibility usually does not occur, even if the baby she carries has positive blood. However, after delivery, the woman has become exposed to the baby’s blood type, and will develop antibodies to the protein her own blood does not carry.

This can significantly impact future pregnancies, and to avoid Rh incompatibility in another pregnancy, a woman with Rh-negative blood is given a shot of RhoGAM, during the 28th week of her first pregnancy. This causes her body to ignore and not become sensitized to the baby’s positive blood type. She is also given another shot right after delivery, or after a miscarriage.


During future pregnancies, these shots may be repeated. Blood tests throughout the pregnancy monitor the presence of Rh antibodies, which might signify a problem. A high amount of Rh antibodies might signify another injection of RhoGAM.

Not all women with negative blood who have a child with a man with positive blood will develop Rh incompatibility with their unborn child. Essentially, each child has a 50% chance of having an incompatible blood type to the mother. It is not, on the surface, easy to type the blood of an unborn child, unless an amniocentesis is performed, or the mother’s blood shows a high number of antibodies to positive blood.

However, it is not worth risking the potentially deadly side effects that can occur to the infant when a mother has Rh incompatibility. Children born to mothers who have an immune response to the child’s blood type may have mental retardation, severe jaundice, hearing loss, speech disorders, heart defects, and a host of other life threatening conditions. It should be noted that the mother is not affected by Rh incompatibility; only the child will show symptoms.

In the US, one usually had one’s blood typed in most states when applying for a marriage license. This is no longer the case, and clearly not all women who are pregnant are married. Because Rh incompatibility is so preventable, it is very important for a pregnant woman to know her blood type and know the potential risk factors.

First, the woman has a negative blood type. If in the past the woman has had a miscarriage or an abortion, Rh incompatibility can still exist. Further, if the woman has ever had a blood transfusion, this should also be noted. The occasional blood transfusion might have been with Rh-positive blood, causing the woman to have already developed antibodies to Rh-positive blood.

Rh incompatibility is yet another reason why regular prenatal care is so important. Since the mother tends not to exhibit any signs of Rh incompatibility, she may be completely unaware that her expected child’s life and health are at risk. Prenatal care quickly evaluates this possible risk and treats it when necessary.


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Post 2

I am Rh negative and my husband is Rh positive.

I've had two pregnancies in the past, but both babies died. The first one had features of IUGR and collodion. I received Rhogam injections. After a Cesarean section on the second pregnancy, the doctor said the fetus was developing Hydrops fetalis and intrauterine death occurred at the eighth month of pregnancy. Tell me what should I do now?

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