Background: Hemolytic disease of the fetus and newborn (HDFN) is due to passively transferred maternal antibodies directed against fetal red blood cell (RBC) antigens and can lead to severe morbidity and mortality. Anti-M is usually a naturally occurring antibody of low clinical significance, although occasionally severe cases of HDFN are seen.
Case Reports: Two M+ sisters are presented, each developing hemolysis during the first 2 weeks of life due to maternal anti-M, resulting in severe anemia and requiring blood transfusion.