OA4-AM24-MN-07 - Red Blood Cell (RBC) Alloimmunization after Intrauterine Transfusion

Background/Case Studies: The reported risk of red blood cell (RBC) alloimmunization after RBC transfusion is estimated to be 0.5-1.5%. Intrauterine transfusion (IUT) is an invasive but critical and life-saving intervention for severe fetal anemia with demonstrated improvement in outcomes. Data is limited regarding the development of additional RBC alloantibodies after IUT. The goal of this study is to characterize patients who developed additional alloantibody(ies) during pregnancy after their first IUT.

Study

Design/Methods: Single quaternary academic medical center, retrospective study of patients who received IUT during pregnancy over an 8-year period, January 1, 2016 – December 31, 2023. This included pregnant patients with prior RBC alloimmunization requiring IUT or diagnosis of fetal anemia from other etiologies. IUTs were performed by the maternal-fetal medicine team and provided washed Group O Rh(D)-negative (rare exceptions), cytomegalovirus-seronegative, freshly irradiated, red blood cells (RBC) that were Hemoglobin S negative and antigen-negative for any maternal antibody.

Results/Findings:

In total, 241 IUTs were performed in 79 pregnancies at our institution during the period from 2016-2023.  An average of 3 IUTs were done per patient and the main indication was RBC alloimmunization (195/241) followed by nonimmune hydrops of unknown etiology (19/241) and fetal alpha thalassemia major (12/241) and others (15/241). Of the 79 pregnant patients receiving IUTs, nineteen percent (15/79) formed a new alloantibody after IUT. Of this patient subgroup, sixty percent (9/15) developed the new alloantibody after their first IUT with a median interval of 18 days. Forty percent of the patients (6/15) that developed new alloantibody after their first IUT had history of prior transfusion and all patients had history of prior pregnancy. New alloantibodies were directed against anti-C (5/15), anti-Jka (4/15), anti-E (3/15), anti-M (1/15), anti-K (1/15) and anti-Wr(a) (1/15). Of the patients who developed a new alloantibody, eighty percent (12/15) had an anterior placenta.

Conclusions: This study showed a higher incidence of RBC alloimmunization in pregnant patients with previous antibodies undergoing IUTs (19%) compared to the incidence of RBC alloimmunization in the general population (0.5-1.5%). The mechanism of further RBC alloimmunization is yet to be determined. Therefore, additional research into the etiologies of maternal RBC alloimmunization is needed and strategies to avoid RBC alloimmunization in patients undergoing IUTs.