Rh incompatibility / Coombs test

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In this article

  • What is Rh incompatibility?
  • The Coombs Test

What is Rh incompatibility?

L'Rh incompatibility it is a reaction of the maternal immune system with production of antibodies that attack the blood cells of the fetus.

This reaction can occur during a second pregnancy in a mom who has a Rh negative blood group with a fetus of Rh positive group if the blood of the two comes into contact, and only if during the previous gestation there had already been the same type of contact, perhaps favored by invasive asamis such as amniocentesis and CVS.

The main possible consequence of Rh incompatibility is the hemolytic disease of the newbornwhich is a condition in which the fetus's red blood cells are damaged or destroyed by maternal antibodies.

Read also: The dictionary of pregnancy

The Coombs test

The search for antibodies responsible for RH incompatibility is carried out through a maternal blood sample that is subjected to the Indirect Coombs test, which is repeated every month in Rh negative pregnant women to check that the reaction does not occur. Also to avoid this reaction, after an invasive procedure, after childbirth or after an abortion, the Rh-negative woman is given immunoglobulin prophylaxis.

The Coombs test has in fact two variants:

  • Direct: it is carried out mainly in the case of a diagnosis of haemolytic disease in the newborn to investigate its aspects 
  • Indirect: it is the most used and that helps to understand if the maternal organism produces specific ones antibodies (anti-D) which damage the red blood cells of the fetus

When to take the test and why

The test is usually ordered at the first gynecological visit in the first trimester of pregnancy, and is then repeated at the 28th week of gestation.

This test is usually ordered especially if the mother has an RH blood type. However, if the patient has a positive RH factor, incompatibility problems are rare, while in the presence of a negative RH factor, several scenarios open up:

  • If the blood type of the father is negative and Indirect Coombs test is negative, the exam is repeated for safety at the 28th week of pregnancy.
  • If the blood group of the father is RH positive, But the Indirect Coombs test is negative, then the test is repeated every month to check that the result remains negative.

It can also happen that, with a mother who has a negative Rh factor, the father's blood type is RH positive and the Coombs test is also positive. Much rarer, however, are the cases in which the maternal-fetal incompatibility is not determined by the RH factor, but by the blood group difference (AB0 incompatibility).

It is normal to prescribe an immunoprophylaxis between the XNUMXth and XNUMXth week of pregnancy, to avoid the possible onset of anti-D antibodies.

Test at Coombs Positive

In the event of a positive result, the types of antibodies present must be identified and checks must also be carried out on the patient's partner.

In a good part of the cases there are no relevant consequences, but there are situations in which the presence of one is highlighted hemolytic disease which can also cause  brain damage to the fetus and even to the perinatal death. However, this case remains very rare.


Read also: What is the Rh factor

Questions and answers

What happens if the Coombs test is positive?

If the Coombs test is positive, it is necessary to analyze the antibodies present and carry out regular checks to monitor the situation.

When is immunoprophylaxis done?

It is normal to prescribe an immunoprophylaxis between the XNUMXth and XNUMXth week of pregnancy, to avoid the possible onset of anti-D antibodies.

What is hemolytic disease of the newborn?

Hemolytic disease of the newborn occurs when the infant's red blood cells are damaged or destroyed by the mother's antibodies.

  • rh factor
  • dictionary of pregnancy
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