Implementing non-invasive RHD genotyping on cell-free foetal DNA from maternal plasma: the Pavia experience.

Background. The occurrence of cell-free foetal DNA in maternal circulation opens new possibilities in non-invasive antenatal diagnosis. Real-time polymerase chain reaction (PCR) analysis is an useful approach to foetal RhD blood group determination, thus being important in the prevention of haemolytic disease of foetus and new-born (HDFN). Study design and methods. Using real-time PCR assays we typed 20 samples of plasma, provided in a blinded fashion, from the International Reference Laboratory, two plasma samples sent by the "2010 Workshop on Molecular Blood Group Genotyping"; seven samples from D-negative mothers at the 16th week of gestation provided by our Hospital as prospective validation cases, and two plasma samples received from the "1 st Collaborative study establishing the sensitivity standard for non-invasive prenatal determination of foetal RHD genotype". To confirm the RHD typing of the seven prospective samples, PCR with sequence specific primers (PCR-SSP) was applied on genomic DNA from amniocytes (5 cases) and paternal peripheral blood (2 cases). Results. The results for the 31 investigated samples showed 100% concordance. Our measurable benefits were: confidence with a new technology, awareness of having gained the European standard level and increased self-assurance regarding the introduction of this typing technique in prenatal diagnostics. Discussion. These results demonstrate the feasibility and accuracy of our validation protocol. RHD typing on cell-free foetal DNA is a procedure which requires particular care and a great degree of expertise for diagnostic use. International collaborations are essential for monitoring the performance of laboratories in the absence of specific quality control programmes.