Blood for intrauterine transfusion (IUT) should meet the following criteria:
- Group O negative or compatible with both maternal and fetal types if known.*
- Negative for the antigens that correspond to the maternal antibodies.
- Crossmatch compatible with maternal serum.
- Irradiated to prevent transfusion-associated graft-versus-host disease (TA-GVHD) in the fetus.
- Cytomegalovirus (CMV) “safe” (leukoreduced and/or CMV seronegative). NOTE: Leukoreduced RBC units are generally considered equivalent to CMV seronegative RBC because CMV is carried intracellularly within leukocytes.
- Negative for HbS to prevent sickling in lower fetal O2 tensions.
Optimally, the blood is less than 7 days old to reduce the risk from accumulated storage lesion products such as potassium and to avoid decreased levels of 2,3-DPG found in older stored blood, which reduces the ability of hemoglobin to deliver oxygen to the tissues. The hematocrit of the unit should generally be 75–85% to deliver maximum numbers of RBCs while minimizing the risk of volume overload in the fetus.
*Some laboratories use red cells that are also K-negative since the K antigen is very immunogenic. This also applies to exchange transfusions.
