Which antibody is most commonly implicated in Rh incompatibility?

• A. Anti-Fya
• B. Anti-Jka
• C. Anti-K
• D. Anti-D

Answer: (D)

Rh incompatibility occurs when an RhD-negative mother is exposed to the D antigen from an RhD-positive fetus, develops anti-D antibodies, and these antibodies cross the placenta in subsequent pregnancies to attack fetal red cells. The D antigen is the most immunogenic among the Rh antigens, so anti-D is far more likely to form after exposure and is the most common antibody causing this incompatibility. The other antibodies listed come from different blood group systems (for example, Fya from Duffy and Jka from Kidd) or the Kell system, and while they can cause hemolytic disease, they are not the typical drivers of Rh incompatibility.