Haemolytic disease of the foetus and new-born due to antibodies against the M-antigen.

Abstract

There are few reports of hemolytic disease of the fetus and the new-born (HDFN) caused by alloantibodies against MNS blood group system, this is because antibodies towards these antigens usually are IgM, which not only are unable to cross the placental circulation, but also react at temperatures below 37°C, having minimal clinical importance. Despite this fact, cases have been reported where the presence of anti-M IgG antibodies caused severe HDFN and even intrauterine death in the presence of maternal-fetal MNS incompatibility, which could have a high clinical impact. The hemolytic pattern observed in these cases is similar to that caused by anti-Kell antibodies. Progressive anemia is mediated and developed through hematopoietic suppression, inducing destruction of bone marrow precursor cells, with the resulting absence of reticulocytes in peripheral blood. This is the case of a woman at 38.5 weeks of gestation who showed a discrepancy between direct and reverse blood type determinations. Blood tests performed to the new-born resulted in a positive direct Coombs test, without the existence of maternal-fetal ABO incompatibility. Further tests were performed and anti-M antibodies in maternal serum screening were found. In this case, we were able to make the final diagnosis mostly due to discrepancy issues in maternal blood. Although anti-M antibodies do not usually play a major role in most HDFN, this case elucidates the importance of identifying the presence of antibodies that can be of crucial importance for preventing HDFN, opening doors to new recommendations regarding screening and prompt treatment of hemolysis in newborns.