P2.I163: Neonatal and Obstetrical Outcomes of Pregnancies Complicated by Alloimmunization

Background: Despite advances in the prevention and treatment of Rh(D) alloimmunization, alloantibodies to Rh(D) and non-Rh(D) red blood cell antigens continue to be detected ~4% of U.S. pregnancies and can result in hemolytic disease of the fetus and newborn (HDFN). Recent reports on HDFN lack granularity and are unable to provide antibody-specific outcomes. The objective of this study was to calculate the frequency of alloimmunization in our large hospital system and summarize the prenatal and postnatal outcomes based on antibody specificity, titer, and other clinical factors.

Methods: We identified all births, during six years, after a positive RBC antibody screen during pregnancy, and summarized their characteristics and outcomes.

Results: Seven hundred seven neonates were born after a positive maternal antibody screen (3.0/1000 live births). In 31 (4%) the positive screen was due to RhIG alone. Of the 676 neonates exposed to alloantibodies, the DAT was positive, showing antigen-positivity and evidence of HDFN, in 174 (37%) of the 466 tested. Neonatal hemolytic disease was most severe with DAT-positive anti-Rh antibodies (c, C, D, e, E). All neonatal RBC transfusions (15) and exchange transfusions (6) were due to anti-Rh alloimmunization. No neonates born to mothers with anti-M, anti-S, anti-Duffy, anti-Kidd A, or anti-Lewis required NICU admission for hyperbilirubinemia or transfusion.

Conclusion: Alloimmunization to Rh-group antibodies continues to cause a majority of the severe HDFN cases in our hospital system. In neonates born to alloimmunized mothers, a positive DAT, showing antigen-positivity, is the best predictor of anemia and hyperbilirubinemia.