Hemolytic disease of the fetus and newborn due to alloanti‐M: three Chinese case reports and a review of the literature

BACKGROUND Alloanti‐M was once regarded as not clinically significant, with a few exceptions in extremely rare cases. However, an increasing number of cases of severe hemolytic disease of the fetus and newborn (HDFN), resulting in fetal hydrops and recurrent abortion caused by alloanti‐M, have been reported mainly in the Asian population. STUDY DESIGN AND METHODS Three pregnant Chinese women with a history of abnormal pregnancy with hydrops fetalis were encountered. During this pregnancy, a series of clinical examinations and an alloantibody identification against RBCs and platelets were conducted. Intrauterine transfusion and postnatal transfusion were then performed in the fetuses. In addition, the HDFN cases caused by alloanti‐M reported in different ethnic groups as well as their clinical and serologic features are also summarized. RESULTS Three pregnant women were identified with an M‐N+ phenotype and IgM mixed with IgG alloanti‐M in serum. Their fetuses were found by ultrasound examination and cord blood testing to have severe anemia. Additionally, an M+N+ phenotype and IgG alloanti‐M were detected in the cord blood of the three fetuses with titers ranging from 1:1 to 1:128. Moreover, low reticulocyte counts and negative direct antiglobulin tests were also shown in two of the fetuses. After receiving intrauterine transfusions and postnatal transfusions several times, these three fetuses eventually survived and then healthfully developed in the follow‐up tracking. CONCLUSION Alloanti‐M immunization can cause severe HDFN with hyporegenerative anemia, often seen in the Asian population, and suppression of erythropoiesis might account for it.