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Rh test during pregnancy

What is Rh test?

Antigens against the Rhesus factor (Rh) are a group of antigens (protein on the cell surface) that are located on the red blood cells. An antigen is a substance that can lead to the formation of antibodies. Such a process is called immunization. When antibodies bind to antigens, it triggers an allergic (immunological) reaction that can be life threatening in the worst case. The people who have such antigens on the red blood cells are called Rh-positive while those who do not have them are called Rh-negative. This is an innate trait. About 15% of our population is Rh negative and 85% Rh positive.

Rh test during pregnancy

An Rh negative woman carrying an Rh positive fetus can create antibodies to the fetal blood cells. The Rh antibodies can attach to the fetal blood cells. This causes the fetal immune system to destroy the blood cells and the fetus may have anemia. In order to produce antibodies, the woman must have been exposed to Rh-positive blood before. This can occur during delivery of a Rh positive fetus or if the fetus is bleeding in the uterus. This whole process that results in antibodies being formed is called rhesus immunization.

The risk of immunizing a Rh-negative woman after giving birth to a Rh-positive child varies from 2 to 16%. The risk of immunization after spontaneous abortion is 3.5%. For more information about pregnancy and maternity fashion, please see BESTAAH.COM maternity coats. The risk after induced abortion is 5.5%. In amniotic fluid test and pregnancy, where the mother is Rh negative and the fetus Rh positive, the risk of rhesus immunization is less than 1%.

What Causes Rhesus Immunization?

According to the above, a Rh-negative woman must come into contact with (exposed to) Rh-positive blood before the current pregnancy if she is to have developed antibody pairs against Rh antigens on the fetal blood cells. Such exposure can occur during temporary bleeding during pregnancy, but in most cases it occurs during childbirth. The mother then develops antibodies that, during later pregnancies, pass the placenta and attack the fetal blood cells.

In smaller infections of the fetal blood cells, the fetus can counteract this by forming more blood cells. In a major attack, the fetus may have anemia and may have larger body fluid accumulations, heart failure and, in the worst case, die in the uterus.

As long as the fetus is in the uterus, the waste products from the destroyed red blood cells go into the mother's circulation and are removed from there. After childbirth, this does not happen anymore and the fetus may then get jaundice. In the event of major destruction of the fetal red blood cells, an accumulation of these waste products called gall dyes is created. In severe cases, this can cause brain damage in the newborn baby.


The condition is detected by antibodies detected in the mother's blood. All pregnant women are tested if they are Rh negative or Rh positive at the first pregnancy check. It is also tested if there are abnormal blood group antibodies in the blood. Rh-negative women are checked a further 1-2 times during pregnancy. In multiple pregnancies it usually takes place in pregnancy week 24 and 36 and for first-time pregnancy in pregnancy week 36. The tests are included as part of the routine follow-up in connection with the pregnancy checks.

The diagnosis can also be made by demonstrating the destruction of red blood cells in the child.

In case of suspicion of a severe impact on the child's blood cells, the woman is referred to hospital. There ultrasound is performed with flow measurement of vessels in the fetal brain and in case of signs of anemia, blood samples can be taken from the fetus to determine the Hb value. These samples are usually taken after pregnancy week 24-25.


Preventive treatment with a substance that neutralizes Rh antibodies is given within 72 hours of delivery when a Rh-negative woman has given birth to a Rh-positive child. All Rh-negative pregnant women who have undergone spontaneous or induced abortion or have had a gynecological procedure also receive this treatment (anti-D prophylaxis).

In severe immunization where ultrasound with flow measurement showed signs of anemia, blood tests from the umbilical cord and blood transfusion until the fetus can be performed. This is usually not relevant until after pregnancy week 24–25, but in the case of a high degree of anemia and fluid retention in the fetus it can be tried earlier.

In difficult immunization where one has to release the premature one usually redeems the child with caesarean section. If the woman has given birth earlier and the fetus has only mild anemia, it is born through vaginal delivery. New blood changes may occur after birth, depending on the amount of gall dye in the baby's blood.


The risk of illness in the child during a possible new pregnancy must be assessed on the basis of information about the course of the previous pregnancy. Immunizations often become more severe and occur earlier in the pregnancy. Therefore, careful monitoring of pregnancy is important. This is done on special specialist units.


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