[Progress of research on biochemistry characteristics of cell-free fetal DNA in maternal plasma and its application].

Cell-free fetal DNA in maternal plasma of pregnant woman, originated from fetal and / or placental cells undergoing apoptosis, is mainly the short-sized DNA fragments of less than 313 base pairs in length for the sake of nuclear endonuclease selectively cleaving fetal DNA during the apoptosis process. The mean cell-free circulating fetal DNA in maternal plasma accounted for 3.4% and 6.2% of plasma total DNA during the early and the late gestation, respectively. Owing to its relative abundance, circulating fetal DNA in maternal plasma has now become the important DNA source for non-invasive prenatal molecular genetic diagnosis and it is widely used in fetal sex-determination, detection of fetal Rh (D) sequence in the plasma of the rhesus-negative woman, fetal aneuploidy detection, fetal STR genotyping and other clinical applications. Cell-free fetal DNA source, concentration, purity, size, distributions and postnatal clearance of fetal DNA in maternal plasma as well as the reported clinical applications are summarized and discussed in this paper. Based on the molecular characteristics of cell-free fetal DNA and the target gene, the using of appropriate molecular diagnosis strategy and experimental design as well as reducing the fragment size of PCR product and adjusting the PCR conditions to the optimum enable the improvement of non-invasive prenatal diagnosis accuracy.