What type of blood should be used for transfusing a fetus?

The appropriate choice for transfusing a fetus is O negative, CMV negative, irradiated, leukocyte poor blood.

Using O negative blood is critical because it is universally accepted for transfusions and minimizes the risk of hemolytic transfusion reactions in the fetus. This is especially important given that the fetus may not have a fully developed immune system, and exposure to different blood types could lead to incompatible reactions.

Additionally, selecting CMV negative blood helps prevent the transmission of cytomegalovirus, which can be particularly harmful to a developing fetus. The irradiation process is important to prevent transfusion-associated graft-versus-host disease (TA-GvHD) by inactivating T-lymphocytes which could mount an immune response in the fetus.

Leukocyte poor blood reduces the risk of transfusion reactions and transmission of infections associated with white blood cells. This is vital in fetal transfusions, as any immune reactions could have severe consequences for the fetus.

Overall, this combination ensures the safest possible transfusion for a fetus in need of blood, accounting for compatibility, infection risk, and immune response considerations.