Anti-M induced severe Hemolytic Disease of the Fetus and Newborn: The role of the Monocyte Monolayer Assay in elucidating the clinical relevance of alloantibodies in pregnancy.

INTRODUCTION: Hemolytic Disease of the Fetus and Newborn (HDFN) is associated with the induction of fetal anemia. Usually, the occurrence of this disease is associated with alloantibodies directed to Rh and K antigens, while severe or fatal cases involving anti-M are rare, especially in non-Asian populations. The Monocyte Monolayer Assay (MMA) is a cellular assay that has been shown to be useful in defining the clinical importance of antibodies.

CASE DESCRIPTION: Severe fetal anemia induced by anti-M was observed in a pregnant 32-year old white Brazilian woman. The immunohematological investigation revealed the presence of two other alloantibodies in the maternal serum. The use of the MMA contributed to elucidating the case, associating only anti-M with the evidenced outcome.

DISCUSSION: The presence of anti-M in pregnant women is generally not a concern, as it is commonly identified as a benign IgM antibody of natural origin. However, it can also be present in its IgG isoform of immune origin, which is associated with both destruction of fetal red cells and suppression of erythropoiesis. There is still no consensus among professionals for the monitoring of pregnant women through the titration of anti-M. In this context, MMA may be useful to clarify the unfavorable outcomes observed in pregnancies of alloimmunized women.

CONCLUSION: The present report describes a rare case of severe fetal anemia associated with maternal anti-M in a Brazilian woman and how MMA assisted to elucidate the clinical relevance of the alloantibodies detected.