RhIg

What is RhIg?
      It a blood derivative that is used to prevent the formation of antibodies to the D antigen in Rh negative persons. Brand name is Rhogam.

Why is it important?
     Prior to the development of RhIg in the 1970s, fetal loss due to anti-D was as high as 46 in 100,000 pregnancies; now it causes 1.6 in 100,000. The D antigen is present in >85% of people and is highly immunogenic. The antibody that forms (anti-D) in a Rh negative person is IgG and can cross the placenta and destroy Rh positive fetal cells causing fetal anemia and/or death.

When is it administered?
    RhIg is given at to Rh negaitve pregnant women at 28 weeks gestation and within 72 hours after delivery.
    Or given to children or women of child-bearing age (< 50 years old) after receiveing Rh positive Red Blood Cells or Platelets.

Why is it administered?
    Since the D antigen is so immunogenic, as little as 2 ml of D positive blood can cause the formation of anti-D. There is the risk during pregnancy to have a fetal maternal bleed which would expose mom to fetal blood and develop this antibody, risks are highest after 28 weeks and at birth.

How does RhIg work?
    RhIg is an passive anti-D that binds to any D positive cells and those cells are then removed by the spleen. This prevents the person's body from recognizing it and making their own anti-D which lasts forever and may compromise future pregnancies. The RhIg generally is gone from the person's system in 3 months.

How much is given?
    One does is considered sufficient for the 28 week dose, but the risk of fetal bleed is greater during birth so another test, Fetal Maternal Hemorrhage Screen, must be performed to determine if more than one dose of RhIg is warranted.

Who is eligible to receive RhIg?
     Person must be Rh negative
     Person must not already have anti-D
     Must be exposed to Rh positive blood (from fetus or blood transfusion)

Are there other ways besides pregnancy and blood transfusion that one can develop Red Cell antibodies?
    Yes. There has been some evidence that sharing needles can expose persons to other peoples blood and potentially make antibodies.

Does RhIg prevent all cases of Fetal anemia due to antibody?
    No. There are many antigens on the Red Blood Cells and if antibodies to these are formed it can cause fetal anemia and/or death. Anti-D is just the most common one. There are no other products currently available to prevent these antibodies from forming.


Rhogam package insert