What is the rhesus factor?
In addition to the AB0 blood group system, the rhesus factor determines whether the blood of different people is "compatible".
The key factor is a protein on the surface of the red blood cells, antigen D. This antigen D is found in around 85% of people in Europe.
These people are rhesus D positive (RhD+). If antigen D is absent, they are Rh negative.
Mother RhD positive - father RhD negative?
If you as a pregnant woman have a positive Rh factor, you will not form any antibodies even if your child is also Rh negative (RhD-) due to a negative Rh factor of the father. Your blood and that of your child "get along".
What if I am RhD negative?
However, about 15% of the European population lacks this protein, they are rhesus D negative.
If you also belong to this group, it again depends on the rhesus factor of the child's father. If the father is also rhesus D-negative, the fetus will also be rhesus D-negative in any case! In this case, no prophylaxis is necessary, since your blood and that of your child are "compatible".
Only if your child is a carrier of antigen D due to the positive rhesus factor of the father (i.e. rhesus D-positive), complications can arise if your blood and that of your child mix.
This can happen at birth or even during pregnancy. Therefore, the administration of anti-D immunoglobulins (rhesus prophylaxis) is necessary!
Risk for the second pregnancy
If you are pregnant for the second time, the antibodies you have already produced will enter your child's circulation via the placenta. If this child is also rhesus D-positive, your antibodies would lead to the degradation of the red blood cells of the fetus and to the illness of the child already before birth or in the worst case even to the abortion.
In this case, rhesus prophylaxis is indeed necessary!
Simply test it!
About 40% of pregnant women with a negative rhesus factor expect a child who is also rhesus D negative. Here, prophylaxis would be completely unnecessary! It is therefore worthwhile to determine the status of the fetus with the help of a simple test.
Good to know!
What happens during rhesus prophylaxis and what are the anti-D immunoglobulins required for this? Why and when does the determination of the fetal rhesus factor make sense?
We have asked for you:
Your rhesus factor is also determined during the blood test, which is part of the standardized preventive medical check-up.
If the mother's test result was rhesus D-negative, until a year ago a blanket anti-D prophylaxis was carried out - without testing whether the unborn child was rhesus D-positive or rhesus D-negative.
With this procedure, about 40% of all rhesus D-negative pregnant women received unnecessary rhesus prophylaxis!
Only if a woman is expecting a rhesus D-positive child can her immune system produce antibodies - and only then is anti-D prophylaxis necessary at all.
By means of rhesus prophylaxis, the fetal red blood cells with the D trait are "removed" from the mother's circulation before rhesus D antibodies can be formed. The build-up of an immune memory (rhesus sensitization) is thus prevented.
Human anti-D immunoglobulins, which are obtained from the blood of sensitized donors, are used for this purpose. Today, 100% of these are imported for the German market from countries that do not belong to the European Economic Area (EEA). This is therefore a rare and scarce resource!
Particularly in the USA there are programs for anti-D procurement, in which Rhesus D-negative donors are sensitized with Rhesus D-positive foreign erythrocytes (for a mostly monetary compensation) in order to form anti-D. This special human plasma is then used to produce anti-D. From this special human plasma, the blood product anti-D immunoglobulins is produced after industrial processing.*
And there is one more factor to consider: Even if anti-D immunoglobulins are infection-proof blood products, transmission of infection as well as side effects due to the preparation and intramuscular administration cannot be 100% excluded.
**Legler, Prof. Tobias J., MD, (2018): Anti-D prophylaxis in RhD-negative women. In: hemotherapy, contributions to transfusion medicine.
Non-invasive prenatal tests to determine the rhesus status of the fetus are a good way of conserving resources by administering the rare anti-D immunoglobulins only when they are actually needed.
From about the 11th week of pregnancy, cell-free genetic material of the fetus can be detected in the maternal blood, the so-called cffDNA. This cell-free fetal DNA is suitable for determining the fetal rhesus factor. This is done with a so-called real-time PCR. This determines the rhesus D status of the fetus.
The concentration of cffDNA increases in the course of pregnancy. Therefore, if there is not enough cffDNA in the maternal blood at the time of the test to provide an unambiguous result, a second test is possible from the 20th week of pregnancy. The costs for both tests are covered by health insurance.
Are you clear about the rhesus factor?
Stay informed!
Pregnancy is an exciting time. A lot of information pours in on the "mother-to-be", and there are always new findings from science and research. We hope that we have been able to give you a brief overview of what the topic of the "rhesus factor" is all about.
Talk to your gynecologist if you have any further questions. We at BAG Diagnostics wish you a joyful pregnancy!
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