Non-Invasive Prenatal RHD Genotyping Using Cell-Free Fetal DNA from Maternal Plasma: An Italian Experience

Background: This study assessed the diagnostic accuracy of a non-invasive approach to fetal RHD genotyping using cell-free fetal DNA in maternal plasma and a combination of methodological strategies. Methods: Real-time PCR (qPCR) was performed on 216 RhD-negative women between weeks 10+0 and 14+6 of gestation (1st qPCR). qPCR was repeated (2nd qPCR) to increase the amount of each sample for analysis, on 95 plasma aliquots that were available from first trimester blood collection (group 1) and on 13 samples that were collected between weeks 18+0 and 25+6 of gestation (group 2). qPCR was specific for exons 5 and 7 of the RHD gene (RHD5 and RHD7). The results were interpreted according to the number of positive replicates of both exons. Results: 1st qPCR: diagnostic accuracy was of 93.3%. Diagnostic accuracy increased from 90.5% (1st qPCR) to 93.7% (2nd qPCR) in group 1 and from 84.6% (1st qPCR) to 92.3% (2nd qPCR) in group 2. These increments were not statistically significant. Conclusion: Our approach to RHD genotyping in early pregnancy yielded high diagnostic accuracy. Increasing the amount of DNA analyzed in each sample did not improve significantly the diagnostic accuracy of the test.