The rhesus blood group feature is not at all dangerous on its own. However, it becomes problematic when an expectant mother is rhesus-negative (that is, has no Rhesus factor in the blood) and the baby in the abdomen rhesus-positive. Because then it can lead to a Rhesus incompatibility. Usually it is only the second child that is affected, if it is rhesus positive again.
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Potentially dangerous: mother negative, baby positive
At the end of each pregnancy (even in the case of miscarriage or abortion), small amounts of the child's blood can enter the mother's bloodstream. Pregnancy with a rhesus-positive child thus affects a rhesus-negative woman like a "wrong" blood transfer! The result: antibodies are formed against the blood group feature "rhesus positive". And they can be very dangerous for a later baby with rhesus-positive blood.
If the mother is Rh-positive, there is basically no danger. The same applies if both - mother and child - lack the Rhesus factor, so both are Rhesus-negative.
What is the Rhesus factor?
Authors: Dr. Hubertus Glaser & Dr. med. med. Jörg Zorn