Candidate for the Lee B. Lusted Student Prize Competition
Purpose: To determine whether cell free fetal DNA (cffDNA) testing should replace antenatal rhesus immune globulin (RhIG) administration as the standard of care in Rhesus D (RhD) negative women.
Methods: A decision analytic model was designed to compare use of cffDNA testing versus antenatal RhIG. Women who were RhD negative, unsensitized, and in a first pregnancy with unknown partner blood type were the basis of the model. Our primary outcome was maternal risk of alloimmunization to RhD in the pregnancy. Sensitivity and specificity of FFD testing were obtained from a meta-analysis and reported as 0.954 (95%CI 0.906-0.978) and 0.986 (95%CI 0.964-0.995) respectively. From the same meta-analysis, positive predictive value was 0.972 and negative predictive value was 0.969. Univariate and bivariate sensitivity analyses, as well as Monte Carlo simulation and threshold analyses, were performed.
Results: Rhesus immune globulin administration is the most effective strategy for preventing alloimmunzation. In a population of 1000 Rhesus negative women, 13 sensitizations would occur with utilization of cffDNA screening for fetal Rhesus type. However, 0.6 sensitizations would occur per 1000 women with routine antenatal administration of antenatal RhIG. Varying the sensitivity of the cffDNA test changed the rate of alloimmunization. Nevertheless, even if a cffDNA test had 100% sensitivity, there was still a higher rate of alloimmunzation compared to standard RhIG. We varied the probability of having an Rh positive fetus from 0 to 1 to account for heterozygosity of Rh in different populations. Our results remained consistent across all probabilities of fetal Rh status.
Conclusion: Adoption of cell fetal free DNA testing in lieu of antenatal rhesus immunoglobulin as the standard of care would result in a 20 fold increase in alloimmunization among RhD negative women. 
See more of: The 33rd Annual Meeting of the Society for Medical Decision Making