Maternal-Fetal Hemorrhage Rh(D) Immune Globulin Dosage

Maternal-Fetal Hemorrhage Rh(D) Immune Globulin Dosage
mL
%
Calculates amount of RhIG to be administered to the mother, at the time of delivery, to prevent hemolytic disease of the fetus and newborn (HDFN).

Why Use

When a mother who is Rh-negative gives birth to a baby who is Rh-positive, there is a possibility that the mother could develop an antibody to the D antigen due to mixing of fetal and maternal blood. The presence of an anti-D leads to a potential risk for HDFN in future pregnancies. Therefore, to prevent HDFN and the formation of an anti-D in the mother, RhIG is given to the mother at 28 weeks and after birth. The amount of RhIG given to the mother after birth is dependent on the amount of fetal-maternal hemorrhage. This formula calculates the amount of fetal-maternal hemorrhage as well as the number of RhIG vials be given to the mother.

When to Use

This calculator should be used to compute the number of RhIG vials to administer to an Rh-negative mother who has not yet developed an anti-D, when she gives birth to an Rh-positive child.

Formula

Number of RhIG vials = fetal cells/total cells counted × maternal blood volume, mL / 30 mL Then, round to the nearest whole number and add 1. Example: Flow cytometry of fetal cells in maternal blood stream = 1.7% Total maternal blood volume = 3,700 mL Volume of fetal blood in maternal blood stream = 3,700 x 0.017 = 62.9 mL Number of RhIG vials = 62.9 / 30 = 2.1 vials --> round down to 2 and add 1 RhIG vials to administer = 3 vials

Pearls / Pitfalls

Calculation of maternal blood volume is an estimation using Nadler’s equation. Fetal cell percentage can be obtained by both flow cytometry or Kleihauer-Betke methodology.

Advice

RhIG should be given to the mother at 28 weeks and after birth.

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