Non-invasive detection of fetal rhesus D status: a comparison between polymerase chain reaction and flow cytometry.

Objective: A non-invasive prenatal determination of the fetal RhD status might be useful for the management of pregnancies in RhD-negative women whose partners are RhD positive.

Methods: Maternal peripheral blood of 32 RhD-negative women (17-24 weeks of gestation) was collected, and circulating fetal cells were enriched by CD71 mini-magnetic activated cell sorting. The RhD status of the fetuses was assessed using multiparametric flow cytometry, and results were compared to those of reverse transcriptase (RT)-polymerase chain reaction (PCR), or PCR, which acted as control. Flow-cytometric study of fetal cells employed monoclonal antibodies directed against CD71, glycophorin A (GPA) and RhD antigens.

Results: The median percentage of CD71- and RhD-positive cells was 0.83% (range 0.14-6.44%), and that of CD71 and GPA-positive cells was 10.07% (range 0.52-45.84%). Flow-cytometric analysis correlated with RT-PCR results of RNA obtained from whole maternal blood. In 1 case, an incorrect result was due to the failure of the amplification of the specific RhD band on RNA extracted from the CD71-positive fraction. In two instances, we observed false-positive results for RhD in PCR of DNA obtained from maternal plasma.

Conclusion: Based on our results, flow-cytometric analysis might be proposed as a clinical tool for the non-invasive prenatal determination of the fetal RhD status independently of fetal gender.