Quantitative analysis of fetal DNA in maternal plasma

Objective To develop real-time quantitative PCR method for measuring the amount of fetal DNA in maternal plasma and the changing patterns of fetal and maternal DNA with the pregnant progress. Methods Fifty-eight women were recruited at 7～42 weeks of gestation with singleton pregnancy determined by ultrasound scan. QIAGEN DNA kits was used to extract fetal DNA from maternal plasma. Fluorescent quantitative PCR(FQ-PCR) were applied to determine the concentration of β-actin and SRY gene in extracted DNA. Results Thirty-seven male fetus were all identified among the 58 pregnant women (100%) and no Y signal was detected in the other 21 pregnancies with female foetus. The median level of fetal DNA in those pregnancies with male foetus was 9.08 copies/ml (3.5～12.8) in early pregnancy,45.41 copies/ml (14.38～76.5) in mid-pregnancy and 300.95 copies/ml (84～840) in late pregnancy. Conclusions The concentration of fetal DNA increases with the progress of pregnancy. Maternal plasma may be valuable in noninvasive prenatal diagnosis.