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Why is Rh-positive blood generally avoided for Rh-negative people who could become pregnant?

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Close-up illustration of multiple human red blood cells with their characteristic disc shape, floating against a red background. — blood group The major component of human blood is the red blood cell.

Rh-positive blood is avoided for Rh-negative individuals of childbearing age because it can trigger the production of anti-Rh antibodies, a process known as sensitization.12

If an Rh-negative person receives Rh-positive blood, their immune system may recognize the foreign Rh antigen and produce antibodies against it. If that person later becomes pregnant with an Rh-positive fetus, these antibodies can cross the placenta and attack the fetus's red blood cells. This destruction of fetal red blood cells, called hemolysis, leads to erythroblastosis fetalis, a condition that can cause severe anemia, jaundice, or even death for the fetus or newborn.13

To prevent this, medical professionals prioritize using Rh-negative blood for these patients unless a transfusion of Rh-positive blood is absolutely necessary to save a life. When exposure to Rh-positive blood occurs, such as after the birth of an Rh-positive infant, clinicians may administer Rh immunoglobulin (often referred to as Rho-GAM) to destroy fetal cells before the mother's immune system can develop permanent antibodies.2134