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large fetal maternal bleed; multiple doses of RhIG

Mabel Adams

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If the Kleihauer calculations are for seven (or more) 300 mcg vials of RhIG (assuming persistent fetal Hgb and weak D have been ruled out), are there precautions for giving that much?  Is it effective?  Is there a number of vials that is just too many? I have heard of concerns for hemolysis, which are sometimes mitigated by spreading out the IV doses and by giving steroids.  I vaguely remember the idea that over a certain number of doses it may be hopeless.  Is the approach different if due to transfusion rather than a FMH? Does anyone have any actual guidelines or evidence?

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There are no data to answer your questions, as far as I know.  It's important to make sure that the fetal cell quantitation is not measuring maternal cells with increased fetal hemoglobin, as this would overestimate the RhIgG dose needed. This is not a problem with some methods (anti-Rh(D) quantitation of fetal cells but can be a problem with acid elution (K-B) staining, for examples.

If there is convincing evidence these are fetal cells, give the correct dose IV even if many vials.  IM injections are cruel and unusual punishment if IV injectables are available.  For patients who are not planning future pregnancies, this should be discussed with the patient.  For sick patients who have received transfusions, we do not infuse RhIgG except for younger women (<40-50) who plan future pregnancies and have a prognosis for survival.  Hemolysis from RhIgG can be a problem at high doses of RhIgG and large transfusion volumes. On balance we usually elect not to give RhIgG to women who have received entire or multiple units of Rh(D) positive red cells.  It's a complex clinical decision with little science to guide us.

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Yup. What Neil said. :) 

We do not give RhIg prophylaxis for women of childbearing age if they have received Rh Pos red cells, but will offer it for Rh pos platelets. Once a full unit of red cells is in, it's a lot to mitigate, and if they're getting 1 unit of Rh pos red cells, they're usually getting MTP and many more Rh pos products. Plus, treatment for anti-D in pregnancy has gotten pretty sophisticated, it's certainly not pleasant for mom, but it can be done. The patient has to survive first! 

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