Multiplex and real-time quantitative PCR on fetal DNA in maternal plasma. A comparison with fetal cells isolated from...

Fetal DNA has recently been detected in maternal plasma by PCR and has shown promise for the prenatal determination of fetal sex or rhesus D. In order to obtain the maximum amount of information from this fetal genetic material, we have devised a sensitive multiplex PCR method to permit simultaneous analysis for both the SRY locus and the rhesus D gene. Our studies show that this technique is very sensitive and specific. In the 22 cases from rhesus D negative women examined, we were able to determine both fetal genotypes correctly. In the parallel enrichment for fetal cells, fetal erythroblasts were only detected in 14 of the 19 cases. Our data also indicate that fetal DNA from rhesus D positive fetuses is present in maternal plasma even after prophylactic anti-D treatment. Furthermore, since fetal cells have been reported to be elevated in pregnancies with aneuploid fetuses, we have quantified the amount of fetal DNA present in the maternal plasma of 10 such affected pregnancies by real-time PCR. Our results indicate that fetal DNA is elevated under such circumstances when compared to gestationally matched normal pregnancies (mean of 7% in aneuploid samples versus 3.5% in normal pregnancies). These results indicate that the quantification of fetal DNA in maternal plasma may be an additional screening tool for pregnancies at risk of bearing an aneuploid fetus.