Feasibility study of using fetal DNA in maternal plasma for non-invasive prenatal diagnosis

The discovery of the presence of fetal genetic material in maternal blood has opened up a new approach to prenatal diagnosis. One approach that has been extensively investigated over the past few decades is the isolation of fetal cells from maternal blood (Herzenberg et al. Proc Natl Acad Sci USA. 1979;76:1453-5; Bianchi et al. Proc Natl Acad Sci USA. 1990;87:3279-83; Cha et al. Prenat Diagn. 2005;25:586-91). As the fetal cells are scarce and the enrichment is of low efficiency, the technique could not be implemented in clinics. In 1997, Lo et al. (Lancet 1997;350(9076):485-7) discovered that cell-free fetal DNA is present in the plasma and serum of pregnant women. This discovery suggests that maternal plasma/serum DNA may be a useful source of material for non-invasive prenatal diagnosis. The objective of our study was to investigate the feasibility of using fetal DNA in maternal plasma for prenatal diagnosis.

Plasma DNA in 277 blood samples of 40 pregnant women at the gestational period from 5 to 40 weeks and 24 h after delivery were extracted by column separation. FQ-PCR was used to amplify the SRY sequence in 237 plasma samples of 30 pregnant women. Fluorescent PCR was used to amplify 9 short tandem repeat loci simultaneously in 40 plasma samples of 10 pregnant women, and genomic DNA samples from their husbands were amplified by the same method.

The fetal SRY sequence could be detected from the 7th week of gestation, with a concentration that increased with progressing gestational age, attaining its highest peak before delivery. Twenty-four hours after delivery, fetal SRY sequence could not be detected in the maternal plasma. The concordance rate of the SRY sequence amplification results of plasma-free DNA, with real fetal gender was 100%. Analysis of maternal plasma samples collected during pregnancy revealed the presence of paternally inherited fetal-specific alleles. Among the 30 collected plasma samples, fetal-specific alleles were detected in 23 plasma DNA samples. The rate of positive results was 76% (23/30), and the frequency of positive results was 6/10 in early pregnancy, 8/10 in middle pregnancy, and 9/10 in late pregnancy. Short tandem repeats could not be detected from the maternal plasma 24 h after delivery.

Fluorescent PCR can be used for amplification of fetal SRY sequence and STRs in maternal plasma to obtain fetal genetic information, which may have implications for non-invasive prenatal diagnosis of certain hereditary diseases.