Anti-D Alloimmunization in Index Pregnancy after Appropriate Rho(D) Immune Globulin Injection in Two Obese Rh-Negative Patients.

The rhesus factor D (RhD)-negative patients who give birth to an RhD-positive newborn or who are otherwise exposed to RhD-positive red blood cells are at risk of developing anti-D antibodies. These antibodies may cause hemolytic disease of the fetus and newborn (HDFN). During pregnancy, prevention of alloimmunization is completed with a Rho(D) immune globulin (RhIg).  We report two cases, where obese patients developed alloimmunization, with high neonatal titers, after appropriate RhIG prophylaxis during the index pregnancy.  Our cases demonstrate cases of anti D-alloimmunization in an index pregnancy, with high neonatal titers. Both patients are obese, with BMI > 35 mg/m . RhIG can be administered via intramuscular or intravenous formulations. Overall, it appears that both formulations are equally effective. The optimal administration, especially with obese women, is not clearly established.Our cases demonstrate that obesity is a risk factor for failure of RhIG, and could lead to an increase in HDFN.