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    Intrauterine RBC Transfusion Dosage

    Estimates volume of donor RBCs needed for intrauterine transfusion (IUT).
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    IMPORTANT

    This dosing tool is intended to assist with calculation, not to provide comprehensive or definitive drug information. Always double-check dosing of any drug and consult your institution's blood bank or a pharmacist as necessary.

    When to Use
    Pearls/Pitfalls
    Why Use
    • Cases of severe fetal anemia, i.e., in hemolytic disease of the fetus and newborn (HDFN).
    • Hemolytic disease of the fetus and newborn (HDFN) can occur when pregnant females have an RBC alloantibody directed against an antigen expressed on fetal RBCs. When alloimmunization is detected during pregnancy, there is generally regular monitoring of both the antibody titer and the fetal middle cerebral artery ultrasound for signs of anemia. In instances of severe fetal anemia, IUT may be used as a treatment and to suppress fetal erythropoiesis.
    • There are other rare indications for IUT that can be determined by specialists in high risk pregnancy.
    • Determining fetal weight and fetal hematocrit both involve ultrasound-based estimations.
    • A pre-transfusion specimen at the time of umbilical vein access can be used for a direct antiglobulin test (DAT), fetal blood type, RBC antigen typing, bilirubin, hemoglobin/hematocrit, and platelet count.
    • Transfused blood for IUT should be group O, negative for antigens against which mother has alloantibodies, crossmatch compatible with mother’s plasma, irradiated, CMV seronegative and/or leukocyte reduced, and hemoglobin S negative.
    • Some experts recommend upper transfusion volume limits for IUT in order to avoid complications such as hyperviscosity and increased umbilical venous pressure. 
    • Hematocrit of tranfused units varies by the type of storage solution, ranging between 55-85%; for specific information, contact your local blood bank or maternal-fetal medicine expert.

    HDFN can have severe consequences, including fetal loss. While IUT can successfully treat HDFN in many instances, it also comes with associated risks. Determining proper volume of RBCs to transfuse to appropriately increase fetal hematocrit is an important step in this process.  

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    Next Steps
    Evidence

    Advice

    In cases of HDFN not due to anti-D, the mother should receive Rh immune globulin after IUT if she is Rh negative in order to prevent D alloimunization.

    Formula

    Transfusion volume, mL = fetoplacental volume, mL × [ Hct(goal) - Hct(initial) ] / Hct(transfused)

    Where fetoplacental volume, mL = fetal weight, g × 0.14 mL/g

    Example calculation:

    • Estimated fetal weight = 1,000 g, Hct(initial) = 20, Hct(goal) = 30, Hct(transfused) = 85
    • ((1000g × 0.14 mL/g) × (0.3-0.2)) / 0.85
    • Transfuse 16.5 mL RBCs

    Evidence Appraisal

    This equation is adapted from the work of Mandelbrot et al in 1988, which used a regression analysis to estimate fetoplacental volume. While the original regression line estimate included a constant (1.046 mL), this is frequently removed in current adaptations due to its relatively small contribution to the overall fetoplacental volume estimate.

    Content Contributors
    • Alex Ryder, MD, PhD
    • Caleb Cheng, MD
    • Christopher Tormey, MD
    Content Contributors
    • Alex Ryder, MD, PhD
    • Caleb Cheng, MD
    • Christopher Tormey, MD