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Rh Immune Globulin (Rho(D) immune globulin)

mLpenguin

• 1 min read
Rh Immune Globulin (Rho(D) immune globulin)
Photo by Pawel Czerwinski / Unsplash

Rh immune globulin is a medication used to prevent alloimmunization in Rh-negative individuals. They prevent the maternal development of anti-D antibodies that can cause hemolytic disease of the fetus and newborn (HDFN) in future Rh-positive pregnancies.

If the mother is Rh- and the fetus is Rh+, the Rh antigens from the fetal circulation can enter the maternal circulation. As a result, it is possible that the mother's immune system will form antibodies against the Rh antigen. This is because the mother's immune system has never seen the Rh antigen before (not been sensitized), and it will be identified as a foreign threat. This becomes a problem as maternal antibodies are able to cross over to the fetus during subsequent pregnancy and can destroy fetal RBCs -> hemolytic disease of the newborn.

This can be prevented with the administration of IgG anti-D antibodies. These bind to the Rh(D)+ fetal RBC and prevents sensitization by the mother by preventing the maternal immune system from recognizing and forming a memory response.

Indications

  • At 28 weeks gestation for all Rh-negative, unsensitized pregnant patients.
  • Within 72 hours after delivery if:
    • Baby is Rh-positive
    • Mother is Rh-negative and not already sensitized
Why at 28 weeks?
This is because the risk of fetal-maternal hemorrhage increases as pregnancy progresses, especially in the third trimester. Studies show small amounts of fetal blood can cross into maternal circulation even without trauma or procedures. 28 weeks is a prophylactic sweet spot where it is long enough to protect through third trimester but early enough to prevent sensitization before delivery.

Dosing

  • Standard dose: 300 µg IM
    • Covers ~30 mL fetal whole blood or 15 mL fetal RBCs
  • If large fetomaternal hemorrhage suspected → Kleihauer-Betke test to calculate additional dose needed
    • Abortion (spontaneous or induced)
    • Ectopic pregnancy
    • Amniocentesis, chorionic villus sampling
    • Abdominal trauma
    • External cephalic version
    • Hydatidiform mole

Contraindications

  • Already sensitized (positive indirect Coombs test) → too late; immune system already primed
  • Rh-positive individuals
      • They are already sensitized