Blood group and Rh factor

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Marie-Ange Demory
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Rh factor in pregnancy

When we are pregnant, among the various tests that are prescribed to us, there is also the analysis of the blood group and the Rh factor, what it is and why it is important to analyze it in pregnancy?

Compatibility of blood groups in pregnancy

In 1900 Landsteiner showed that human red blood cells have on their surface two antigens that he indicated with A and B which determine the belonging of each of us to a blood group:

  • Group A antigen
  • Group B antigen
  • Both group AB antigens
  • No group O antigen

And he also identified in the plasma of the individuals of:

  • Group A beta agglutinin (anti-B) capable of destroying the red blood cells of groups B and AB.
  • Group B agglutinin alpha (anti-A) capable of destroying red blood cells of groups A and AB.
  • Group O both agglutinins.
  • Group AB none.   

antigens we mean any substance recognized as foreign to the organism and capable of inducing a specific immune reaction, which manifests itself with the activation of particular cells, the T lymphocytes, and / or with the production of antibodies.

This type of recognition allows the prevention of the onset of diseases when we come into contact with pathogenic microorganisms, since it causes their elimination before they can multiply significantly and cause damage. The Rh factor is nothing more than a group of molecules (antigens) present on the surface of red blood cells, if it is present it is called Rh-positive factor, if instead there is no it is called Rh-negative factor.

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Rh factor, genetics

Normally we are not interested in knowing if our Rh factor is positive or negative, but during pregnancy this fact takes on great importance.

If mom's blood type is A, B or AB positive, it is not necessary to know the husband's group. If the group is 0 positive, it is advisable that the husband also carry out the examination because if it were A, B or AB the child could present at birth AB0 incompatibility jaundice. It is not a serious pathology, but if it occurs, knowing the father's group accelerates diagnosis times.

Blood grouping is performed during pregnancy to ascertain compatibility between mother and father. Let's see the various possibilities.

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Positive rh factor

If both the mum è Rh-positive and so is the father, there is no complication and no therapy to be done.

If to be positive is only the father while the mother is Rh-negative, the probability that the fetus is Rh-positive is 50%. The Rh negative mother does not have the antibodies against the Rh factor, but develops them in contact with the Rh-positive blood of the fetus (phenomenon called isoimmunization). As Drug and Treatment explains, the problem does not occur with the first pregnancy, but in the next oneIf the second child is still Rh-positive, the mother's antibodies produced during the first pregnancy will attack the fetus's red blood cells.

What if mom is Rh-negative? The Coombs test every month to detect the presence of antibodies on the surface of red or free blood cells in the serum and there are specific pharmacological treatments, such as immunoglobulin Rh which prevent the body from making antibodies to the Rh factor. Rh-negative women will need to take this drug at each pregnancy in case the fetus is Rh-positive. 

Rh negative factor from positive parents

The transmission of genes follows complicated paths because both the father and the mother can pass on dominant genes and recessive genes to the child. This can happen if two parents have Rh-positive but the baby is born with a negative factor (an event that happens in one out of four cases). Why does this happen? Because both parents are carriers of the negative gene even if the dominant gene is the positive one.

Negative Rh factor

Rh-negative women who conceive a child with Rh-positive are at risk, so if the mother is Rh-negative, you need to know the blood type of the father. If this is Rh-positive, the fetus could itself be Rh-positive and, therefore, could be created an Rh incompatibility between mother and fetus. In this case, as we said, the mother makes antibodies against the Rh antigen which pass through the placenta and destroy the red blood cells of the fetus, causing thehemolytic anemia of the newborn.

From here we understand perfectly the importance of knowing the blood groups and Rh factors of both parents. In general, a blood test is sufficient and possibly, if you prove to be rh-negative, your doctor will prescribe a antibody test to see if there are antibodies in your blood (developed as a result of some exposure to the Rh factor). If the antibody test is negative, the father will also have to do a blood group analysis and if it comes out Rh-positive then there will be a 50% chance that the baby will be born Rh-positive and therefore of incompatibility with Mother.

As we said it is not a serious thing, there are procedures and iter clinics now common practice to deal with this incompatibility, the important thing is to be aware of it.

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