Objective      To study the level and segments of free DNA molecules in maternal plasma by fluorescence quantitative PCR.       Methods      Free DNA was isolated from plasma of 42 pregnant women with a gestational period of 16-20 weeks and 40 non-pregnant women undergoing physical examination in our department in August 2011. Different segments of the target genes

leptin and SRY

were specifically amplified. The length of amplified leptin gene segments was 80 bp and 202 bp respectively

while that of the SRY gene segments was 83 bp and 206 bp respectively. Their intact gene segments and DNA level were observed.         Results      The average DNA level in 80 bp and 202 bp segments of leptin gene was significantly higher in maternal group than control group (681 copies/mlvs157 copies/ml

439 copies/mlvs91 copies/ml

P0.01）

while the average DNA level in 83 bp and 206 bp segments of SRY gene was significantly lower than that in 80 bp and 202 bp segments of leptin gene in maternal group than in control group (94 copies/ml and 80 copies/mlvs 681 copies/ml and 439 copies/ml

P0.01）.       Conclusion      The free DNA level is significantly higher in pregnant women than in non-pregnant women and fetus. The difference in free DNA molecules of maternal and fetal plasma found in this study provides a novel idea for the enrichment of fetal DNA and the evidence for research on fetal molecular makers and noninvasive prenatal diagnosis.