(P-TS-55) Fetal Anemia Due to RhD Alloimmunization is Not Associated with First-Trimester Pregnancy Losses in a Cohort of Patients Requiring In Utero Transfusions

Background/Case Studies:
Approximately 10% of pregnant patients with RhD alloimmunization will require in utero transfusions (IUT) due to severe fetal anemia. One of the mainstays of prevention is Rh immunoglobulin (RhIg) administration during pregnancy and immediately postpartum when the newborn is found to be RhD positive. There remains controversy, however, as to whether RhIg administration is of value in first-trimester pregnancy losses. This study utilizes chart review of a cohort of pregnancies complicated by RhD alloimmunization requiring IUTs to identify potential events leading to alloimmunization, including previous first-trimester pregnancy loss.

Study

Design/Methods: This study utilizes a retrospective cohort study of all pregnant people requiring IUT due to complications of RhD alloimmunization at a single center between December 2015 and March 2025. Chart review of electronic medical records identified the event leading to RhD alloimmunization via interrogation of transfusion history and review of prior pregnancy data, as well as other pertinent details of the pregnancy, such as other antibodies identified, gestational age at delivery, and mode of delivery.

Results/Findings: Between December 1, 2015, and March 31, 2025, 42 patients were identified as requiring IUT due to fetal anemia from RhD alloimmunization. In 30 (71%) individuals, prior pregnancies show evidence of alloimmunization, either by the development of alloantibodies over the course of a previous pregnancy or diagnosis of hemolytic disease of the fetus or newborn in a previous pregnancy. 3 (7%) individuals received RhIg but later developed anti-D antibodies, requiring IUT in the current pregnancy. 3 (7%) additional individuals had no evidence of alloantibodies in previous pregnancies, but these deliveries were complicated by postpartum hemorrhages requiring transfusion. The identifying cause is unknown in 6 cases, including 2 (5%) who were nulliparous with no known pregnancy losses nor transfusion history, and 2 (5%) who had only had a prior pregnancy with an RhD negative child (no postpartum RhIg) and no transfusion history.

Conclusions:
In this cohort of pregnant people requiring IUT due to RhD alloimmunization, the event leading to alloimmunization is often a prior pregnancy. However, review of medical records identifies the development of antibodies occurring over the course of a pregnancy, with evidence of alloantibodies in the second or early third trimester. Although limited by a small cohort, this study adds evidence to the current debate regarding the utility of first-trimester RhIg administration following pregnancy loss by showing the absence of first-trimester loss as a cause of RhD alloimmunization among a group of pregnant individuals requiring IUT in pregnancy.