Rh incompatibility: what it is and what dangers it has for pregnancy

One of the first and most important tests that a pregnant woman should do is the blood test. This basic test determines what blood type she has and what her Rh factor is. And it is that the Rh factor will play an important role in the health of the baby .

The Rh factor is a protein present in cells, and depending on their blood type, each person has proteins specific to that blood type on the surface of red blood cells. There are four blood groups: A, B, AB and O.

In turn, each of the four blood groups is classified according to the presence or not on the surface of red blood cells of another protein that determines the Rh factor. If the person is a carrier of this protein, they are Rh positive; if she is not a carrier, she is Rh negative. Check out more interesting articles on our site The Blog.

Most of the population, 85%, has that particular sequence of amino acids that in common language is usually called Rh+. There are many possible combinations depending on the Rhs of the parents, but Rh sensitization or Rh incompatibility can only occur when the mother is Rh negative and the father is Rh positive .

Rh negative mother and Rh positive father

Of all the possible combinations, the risk exists when the blood group of the Rh- woman and that of the Rh+ man are combined, although there would be no risk if the baby inherits the Rh- from the mother .

But when an Rh-negative woman and an Rh-positive man conceive a child, there is a chance that the baby will have health problems. It is possible that the developing baby inside the mother who is Rh negative has Rh positive blood that she inherited from the father.

About half of children with an Rh-negative mother and an Rh-positive father are Rh-positive.

It should be noted that the possible adverse effects would not normally occur in the first pregnancy, but in the following ones.

There is no risk of Rh incompatibility in the first pregnancy

The mother is normally not sensitized in the first pregnancy, but in the second or subsequent ones; For these purposes, any previous pregnancy is considered to be the first, even if it has not reached term.

This means that Rh incompatibility is usually not a problem in a first pregnancy because, unless there is some kind of abnormality, blood from the fetus does not enter the mother’s circulatory system during pregnancy. .

However, during childbirth, the mother’s and baby’s blood can mix. If this happens, the mother’s body recognizes the Rh protein as a foreign substance and begins to produce antibodies (protein molecules in the immune system that recognize, and then destroy, foreign substances) to attack the Rh proteins that enter her blood.

Pregnant Rh-negative women can also come into contact with Rh protein (something that could produce antibodies) in Rh-positive blood transfusions, miscarriages, and extrauterine pregnancies.

During subsequent pregnancies, red blood cells from the fetus can pass into the mother’s bloodstream as she feeds the fetus through the placenta.

Rh antibodies are not harmless in subsequent pregnancies , since if the mother conceives an Rh+ baby, the woman’s body will now recognize the Rh proteins as foreign bodies. Then her antibodies will go into the baby’s bloodstream to attack those cells.

What is the Coombs Test?

That is why it is so important to detect from the beginning of pregnancy if the mother has begun to generate antibodies. To do this, a test called the indirect Coombs test, also known as the indirect antiglobulin test, is performed.

It is a non-invasive test that is performed through a blood sample from the mother in the first trimester, in the 8th or 9th week, and is repeated in the second trimester, in the 26th week of pregnancy.

Consequences of Rh incompatibility for the fetus

If the mother’s body begins this “attack” it can lead to dilation and rupture of the baby’s red blood cells. When this condition occurs, it is known as hemolytic disease or Rh disease of the newborn .

This disease, whose scientific name is “erythroblastosis fetalis”, is a blood disorder in which, given the different blood types, a mother produces antibodies during pregnancy that attack the red blood cells of her own fetus.

The name erythroblastosis is due to the appearance in the circulating blood of a high number of erythroblasts, which are precursors of red blood cells, which have been released into the circulation.

The severity of this condition can vary widely. In some cases, the baby has no symptoms of the disease; in other cases it can lead to the death of the baby before or shortly after birth. This disorder can be treated in utero (before the baby is born) by intrauterine transfusion.

When the baby is born, signs that may present as signs of Rh incompatibility are: enlarged liver or spleen, generalized swelling, jaundice, and anemia. After birth, depending on the severity of the condition, a blood transfusion is usually necessary.

What is the treatment for RH incompatibility?

In the past it was much more complex, but today the treatment is very simple. To prevent sensitivity caused by Rh incompatibility, special immunoglobulins called RhoGAM are used .

Whether the test results are positive or negative, if the father is Rh positive and the mother negative, the pregnant woman receives an injection of anti-D gamma globulin around week 28 to prevent the production of antibodies during childbirth, when the The mother’s blood may be mixed with the baby’s, and another injection within 72 hours after delivery to prevent the mother from making antibodies.

If the woman has already developed the antibodies, the pregnancy should be followed closely to check that the Rh levels are not too high. Only in exceptional cases, if the incompatibility is very serious and can put the baby at risk, are blood transfusions called exchange transfusions performed during pregnancy and after delivery.

Exchange transfusions replace the baby’s blood with Rh-negative red blood cells to minimize the damage that can be caused by the circulation of Rh antibodies already present in your bloodstream.


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