A single‐center, retrospective analysis of 17 cases of hemolytic disease of the fetus and newborn caused by anti‐M antibodies

We aimed to summarize the laboratory findings and clinical features of hemolytic disease of the fetus and newborn (HDFN).We retrospectively analyzed the data for 17 infants with anti-M-induced HDFN (anti-M-HDFN) diagnosed between June 2013 and May 2019. Their maternal history, neonatal diagnosis on admission, and laboratory test results were compared with those of 15 infants with HDFN involving the ABO blood group system, 15 infants with HDFN involving the Rh system, and 15 premature infants.In the anti-M-HDFN group, 94.12% (16/17), 35.29% (6/17), and 17.65% (3/17) had free antibodies in plasma, a positive direct antiglobulin test, and a positive elution test, respectively. In 12 infants, free antibody reactions were stronger at 4°C than at 37°C, and the antibody titer at 4°C ranged from 1 to 512. All 17 infants with anti-M-HDFN developed anemia: 14 were treated with blood transfusion and 1 with neonatal exchange transfusion. Sixteen infants improved, and one died. Anti-M-HDFN had a higher rate of maternal stillbirth, lower gestational age, lower birthweight, and higher incidence of respiratory distress than other HDFN types.Anti-M may cause HDFN. It may present with varying degrees of anemia, low regenerative anemia, and low bilirubin levels. In addition, infants with anti-M-HDFN may have a negative elution test and direct antiglobulin test. These tests are helpful in examining antibody responses at a low temperature of 4°C.