After anti-D, the antibodies that are most often associated with HDFN include:
- anti-Fya (rarely)
- anti-Jka (rarely)
- anti-M,-N,-S,-s,-U (all rarely)
Of these antibodies, anti-K, anti-c, and anti-E are more common causes. Anti-K is frequently associated with a severe form of HDFN due to the ability of the antibody to suppress fetal erythropoiesis in addition to causing hemolysis. Anti-c has also been known to cause severe HDFN.
Antibodies to low frequency antigens have also been known to cause HDFN, albeit rarely. Examples include anti-Mia, -Dia, -Wra and anti-Rd. In such cases the maternal antibody screen is usually negative and the only unexpected test is a positive DAT on the newborn.
Although it is frequently present in the serum of pregnant women, anti-Lea is not generally associated with HDFN for two reasons; anti-Lea is most often IgM and therefore it does not cross the placenta. In addition, the Lewis system antigens are not well developed at birth.