Quantitation of fetal DNA in maternal serum in normal and aneuploid pregnancies

We investigated whether the amount of circulating cell-free fetal DNA in ma ternal 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 unde rgoing amniocentesis. In total, we examined 70 samples consisting of 55 cas es 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 cas es with 46,XX which were used as negative controls. We measured the concent ration of the SRY sequence as a molecular marker for fetal DNA. The SRY seq uence was detectable and measurable when the fetuses were male except for o ne case with 47,XY,+18 This case showed fetal growth retardation and bradyc ardia. 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 pregn ancies 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 be tween pregnancies with fetuses of normal karyotype and those with fetuses o f abnormal karyotype.