(P-TS-22) Case Series: RhIG Treatment Failure

Rh(D) immunoglobulin (RhIG) is indicated for administration to D negative pregnant women to prevent alloimmunization against the D antigen. RhIG is routinely provided for antenatal prophylaxis at 28 weeks of gestation, and it is additionally indicated in the setting of fetomaternal hemorrhage (FMH). Prophylactic administration of RhIG is typically limited to a single standard dose (300µg), whereas RhIG dosage is individually calculated in the setting of FMH.

Investigators previously demonstrated that elevated maternal BMI is correlated with decreased serum anti-D concentrations following administration of standard doses of RhIG. Elevated maternal BMI is additionally correlated with increased incidence of RhIG treatment failure in preventing alloimmunization against the D antigen.

Presented here is a brief case series illustrating two occurrences of RhIG treatment failure in pregnant patients with elevated BMI’s.

The first case is a 29-year-old G1P0 woman with a BMI during pregnancy of 44 kg/m². Routine type and screen performed in the first trimester demonstrated that she was type O- with a negative antibody screen. She received a standard dose of RhIG (Rhophylac) at 28 weeks gestation for prophylaxis. She presented to the hospital at 39 weeks gestation for cesarean section, and a repeat type and screen demonstrated high titer anti-D (1:128).
The second case is a 33-year-old G3P2 woman with a BMI during pregnancy of 39 kg/m² who notably received RhIG for all standard indications during her first two pregnancies. Routine type and screen performed in the first trimester of her third pregnancy demonstrated that she was type B- with a positive antibody screen of undetermined significance. She remained a candidate for RhIG administration during her pregnancy, and a standard dose of RhIG was administered prophylactically at 27 weeks gestation. Labor was induced at 40 weeks gestation, and a postpartum repeat type and screen demonstrated high titer anti-D (1:512).

Given the high titer of anti-D in both postpartum patient samples, these results were favored to represent true alloimmunization against the D antigen.

Study

Design/Methods: Chart review was conducted to gather patient data regarding pregnancy course, RhIG dosing timelines, and serologic findings.

Results/Findings: Both of the encountered patients experienced RhIG treatment failure in the setting of significantly elevated BMI’s during pregnancy. The patients had BMI’s of 44 kg/m² and 39 kg/m², respectively. Subsequent anti-D titers following alloimmunization were 1:128 and 1:512, respectively.


Conclusions: The presented cases provide additional evidence that elevated maternal BMI’s may correlate with failure of RhIG treatment when standard dosages are utilized. Hospital blood banks that routinely support RhIG administration for this indication may consider implementing policies for modifying RhIG dosages for women with elevated BMI’s.