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Why is Rh-positive blood avoided for Rh-negative females who may become pregnant?

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Blood transfusion — blood transfusion Depiction of a direct blood transfusion performed in 1882.

Rh-positive blood is avoided for Rh-negative females of childbearing age because it can lead to sensitization, a process where the recipient's immune system develops anti-Rh antibodies in response to the foreign Rh antigen.12

If an Rh-negative woman is transfused with Rh-positive blood, she may form these antibodies. If she later becomes pregnant with an Rh-positive fetus, these pre-existing antibodies can cross the placenta and attack the fetal red blood cells. This destruction of fetal blood, known as hemolysis, causes erythroblastosis fetalis—a condition that can lead to severe anemia, brain damage, or death for the infant.1234

Because this immune response creates a permanent risk for future pregnancies, medical professionals prioritize using Rh-negative blood for these patients unless a transfusion is life-saving and no other options are available.12