531: Anti-Rh(D) Alloimmunization: Outcomes at a single institution

Abstract

To review outcomes in gravidas with anti-Rh(D) alloimmunization in their first alloimmunized pregnancy. Data collected from pregnancies complicated by anti-Rh(D) alloimmunization at The Ohio State University from 1969 through June 2017 was reviewed retrospectively. Only the first sensitized pregnancy for each patient was included in this descriptive study, and we excluded women with more than one red blood cell antibody. Antibody titers were reviewed, with a critical titer defined as >16. Significant hemolytic disease of the fetus and newborn (HDFN) was diagnosed in the setting of intrauterine fetal demise (IUFD), hydrops fetalis, need for intrauterine transfusions (IUTs), and need for neonatal red blood cell transfusions (exchange or simple). Of the 590 patients who met the inclusion criteria, 178 (31.2%) maintained an anti-D titer <16. A critical titer was identified in 392 patients (68.8%), 234 (57.7%) of whom did not develop HDFN. Outcomes for the 178 pregnancies (31.2% of the entire cohort) complicated by HDFN are depicted in Figure 1. Of the 173 women who reached a critical titer in the first or second trimester, 82 (47.4%) developed HDFN while this disease occurred in only 76 (34.7%) of the 219 patients who achieved a critical titer in the third trimester (RR 1.37, 95% CI 1.07 to 1.74). A critical titer was identified at an average gestational age of 26 weeks and 3 days in women with HDFN compared to 28 weeks and 5 days in patients without disease. Alloimmunization to the Rh(D) antigen is relatively uncommon in the age of Rh immune globulin (RhIg) prophylaxis, but cases persist due to unrecognized fetomaternal bleeding and failure to properly administer prophylaxis. Essentially, in a patient’s first pregnancy complicated by anti-Rh(D) alloimmunization, approximately 1/3 of women will maintain a low antibody titer, 1/3 will reach a critical titer without developing sequelae, and 1/3 will develop significant HDFN. Understanding the natural history of this disease allows physicians to provide appropriate counseling about the likelihood of related outcomes.