RhoGAM Dose Calculator for Fetal Maternal Hemorrhage

Determines the Rh(D) Immune Globulin to administer to Rh negative mother to prevent hemolytic disease of the fetus and newborn (HDFN).

Refer to the text below the tool for more information about feto maternal hemorrhage prevention in Rh negative mothers during pregnancy and at birth.

In order to prevent hemolytic disease of the fetus and newborn (HDFN) and decrease the risk of erythroblastosis fetalis in a second pregnancy, Rh-negative mothers giving birth to an Rh-positive child are administered at birth a quantity of Rh[D] immune globulin.

  • Maternal blood volume (in Litres) can be estimated via Nadler’s formula from height and weight (3561 x Height in m3 + 0.03308 x Weight in kgs + 0.1833)
  • Fetal cell percentage can be obtained by both flow cytometry or Kleihauer-Betke methodology.
  • Number of RhIG vials of 300 µg RhIG = fetal cells/total cells counted × maternal blood volume (mL) / 30 mL then rounded to nearest whole number and added 1.
Is Maternal Blood Volume Known?
Maternal Blood Volume
Fetal Cells*
*Flow cytometry of fetal cells in maternal blood stream
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Administering Rh(D) Immune Globulin

Rh-negative mothers giving birth to Rh-positive babies are at risk of developing an antibody to the D antigen due to the mixing of fetal and maternal blood (during pregnancy and/or birth). The presence of anti-D leads to a risk of hemolytic disease of the fetus and newborn (HDFN) in future pregnancies.

RhIG should be given to the mother during antenatal care at 28 weeks gestation and after birth. The amount of RhIG (brand names RhoGam, WinRho, RhesuGam etc) is dependent on the amount of fetal-maternal hemorrhage (also known as fetal bleed).

  • Volume of fetal bleed: % fetal cells x maternal blood volume in mL
  • Maternal blood volume (in Litres) can be estimated via Nadler’s formula from height and weight (0.3561 x Height in m3 + 0.03308 x Weight in kgs + 0.1833)
  • Fetal cell percentage can be obtained by both flow cytometry or Kleihauer-Betke methodology.
  • Number of vials of 300 µg RhIG (1500 IU) = fetal cells/total cells counted × maternal blood volume (mL) / 30 mL then rounded to nearest whole number and added 1.

Rh(D) immune globulin is made up of antibodies to the antigen Rh(D) present on some red blood cells and its action is to block the immune system from recognizing this antigen.

RhoGam and other brand formulations of RhIG are prescribed for the prevention of Rh Sensitization in Rh negative mother. Aside from the routine dosing (GA: 28 weeks & birth), it may be administered to mitigate risks in uterine bleeding or trauma in Rh negative mothers.

 

References

Kennedy, M, Delaney M, Scrape S. Perinatal issues in transfusion practice. In: Fung M, Grossman B, Hillyer C, Westhoff C, eds. Technical Manual.18th ed. Bethesda, MD: AABB; 2014:561–569.

Legler TJ. RhIg for the prevention Rh immunization and IVIg for the treatment of affected neonates. Transfus Apher Sci. 2020:102950.

Specialty: Obstetrics Gynecology

Article By: Denise Nedea

Published On: November 7, 2020 · 12:00 AM

Last Checked: November 7, 2020

Next Review: November 7, 2025