Abstract： Objective To investigate the methods and clinical significance of detecting PLAC4 and COL6A1 gene on fetal chromosome 21 from maternal peripheral blood. Methods From Oct. 2008 to Nov. 2009 30 normal pregnancies in Weifang People's Hospital were selected as pregnant group, and 9 nonpregnant women were selected as control group. Quantitative real-time PCR was used to determine transcript levels of the target genes ( PLAC4 and COL6A1 ) in blood samples. Correlation between the expression level and gestational age was analyzed. Results ( 1 ) PLAG4 mRNA was detected in peripheral blood of all pregnant women. Its maximum level was 12. 760 × 103 copies/ml, whereas the minimum was 2. 105 × 103 copies/ml, and the average value is 6. 612 × 103 copies/ml. In control group the PLAC4 mRNA could not be detected. There was statistically significant difference ( P ＜ 0. 01 ) between the two groups. ( 2 ) COL6A1 mRNA is detected in pregnant group and control group, and the concentration was 6. 847 × 103 copies/ml and 7. 322 × 103 copies/ml respectively, with no statistically significant difference ( P ＞ 0. 05 ). ( 3 ) Correlation analysis: there was no relationship between the level of PLAC4, COL6A1 mRNA and the gestational age, the correlation coefficients (r) were 0. 29 and 0. 31, and the P values were 0. 121 and 0. 168 respectively. Conclusions COL6A1 mRNA can be detected in both pregnant group and control group, so it is not specific for pregnancy. PLAC4 mRNA can be detected only in pregnant women, so it has specificity in pregnancy and can be a discriminative marker gene for prenatal dignosis of trisomy 21 fetuses.