Non‐invasive foetal RhD genotyping: A strategy for rationalizing anti‐D immunoglobulin prophylaxis in RhD ‐negative pregnant women at the Hospital Italiano de Buenos Aires

Background and Objectives The administration of anti‐D immunoglobulin achieved a significant reduction in the mortality of haemolytic disease of the foetus and the newborn due to RhD sensitization. Between 30% and 40% of this group of pregnant women, carriers of an RhD‐negative foetus, would unnecessarily receive a high‐cost drug, exposing them to the risks of a blood derivative. The aim of the study was to assess the accuracy of non‐invasive foetal RhD genotyping at different weeks of pregnancy, to allow it to be used to determine appropriate anti‐D administration. Materials and Methods In this cross‐sectional cohort study of foetal RhD genotyping, determined from cell‐free foetal DNA (cffDNA) between weeks 8 and 30 of gestation, 270 samples from RhD‐negative pregnant women were examined. Foetal Rh status was determined by multiplex PCR in real time, to detect targeting exons 5, 7, and 10 of the RHD gene and the SRY gene (a Y‐chromosome‐specific marker used to confirm male foetal sex). Results The performance diagnostic of the foetal RhD screen test offered a sensitivity of 100% (95% confidence interval [CI]: 98.03%–100%), a specificity of 100% (95% CI: 96.3%–100%) and an accuracy of 100%. The prevalence of RhD‐negative newborns in RhD‐negative pregnant women was 32.5%. Conclusion The results of the study reveal that the strategy of combining three RhD exons to determine foetal RhD status is reliable, with 100% accuracy. Prenatal diagnosis showed that 32.5% of newborns were RhD negative. Using this strategy, a decrease in the use of anti‐D immunoglobulin is expected.