How does Rhogam prevent erythroblastosis fetalis (HDN, hemolytic disease of the newborn)?

Question

anonymous · Answer

Rhogam is human antibody to the Rh antigen. If any fetal blood cells escape into the maternal circulation, Rhogam binds to the Rh antigen and makes it "invisible" to the mother's immune system. One dose at 28 weeks, and another at the time of delivery is enough to prevent the mother becoming sensitized. Additional injections are given whenever there is any other chance of fetal cells leaking into the maternal circulation, such as at the time of miscarriage, ectopic pregnancy, or episodes of significant vaginal bleeding.

anonymous · Answer

Rho(D) Immune Globulin(brand name RhoGAM) is a solution of IgG anti-D (anti-RhD) antibodies that bind to, and lead to the destruction of, fetal Rh D positive red blood cells that have passed from the fetal circulation to the maternal circulation.
This is passive immunity and the effect of the immunity will wear off after about 4 to 6 weeks (or longer depending on injected dose) as the anti-Rh antibodies gradually decline to zero in the maternal blood.