Which type of antibody can cause hemolytic disease of the fetus and newborn (HDFN) in any pregnancy?

The correct answer is Anti-A,B. This type of antibody is significant because it can lead to hemolytic disease of the fetus and newborn (HDFN) in situations where the mother has blood group O, which naturally contains both anti-A and anti-B antibodies. In such cases, if the fetus has blood group A, B, or AB, these maternal antibodies can cross the placenta during pregnancy and attack the fetal red blood cells, resulting in hemolysis.

This contrasts with anti-RhD antibodies, which are specific to individuals with the RhD negative blood type and primarily pose a risk in RhD-sensitized pregnancies. Anti-A and Anti-B antibodies also act specifically against certain blood groups but are less likely to cause HDFN in every pregnancy compared to Anti-A,B antibodies, as these are not restricted by individual's blood group but can react to the presence of either A or B antigens in the fetus.