2. What is the involvement of Rh blood group system in Hemolytic Disease of the Fetus and Newborn (HDFN)?

- Historically, Rh blood group system has been known to cause hemolytic disease of the fetus and newborn. Anti-D was a frequent cause of fetal death before the implementation of Rh-immune globulin therapy. This was to be expected because while 15% of the population is Rh-negative, 85% of the population is Rh-positive; therefore, the likelihood an Rh-negative woman is carrying an Rh-positive fetus is significant. HDFN caused by Rh antibodies is often severe because the Rh antigens are well developed on fetal cells, and Rh antibodies are primarily IgG, which readily cross the placenta.