Quantitation of fetal DNA in maternal serum in normal and aneuploid prenancies.
We investigated whether the amount of circulating cell-free fetal DNA in maternal serum is influenced by fetal karyotype, using real-time quantitative polymerase chain reaction assay. Serum samples were obtained from pregnant women at gestational ages ranging from 15 to 17 weeks, prior to their undergoing amniocentesis. In total, we examined 70 samples consisting of 55 cases of pregnancy with 46,XY, 5 cases with 47,XY,+21, 3 cases with 47,XY,+18, a single case with 46,XY,dup(1) and 2 cases with twins of 46,XY, and 4 cases with 46,XX which were used as negative controls. We measured the concentration of the SRY sequence as a molecular marker for fetal DNA. The SRY sequence was detectable and measurable when the fetuses were male except for one case with 47,XY,+18. This case showed fetal growth retardation and bradycardia. No amplification signals of the SRY sequence were detected when the fetuses were female. The mean concentration of fetal DNA in maternal serum was 31.5 copies/ml in the pregnancy with 46,XY, 23.5 copies/ml in the pregnancies with 47,XY,+21 and 21.5 copies/ml in the pregnancies with 46,XY,+18. There were no significant differences in the concentration of fetal DNA between pregnancies with fetuses of normal karyotype and those with fetuses of abnormal karyotype.