ABSTRACT
<p><b>OBJECTIVE</b>To study the feasibility of using free fetal DNA in maternal plasma for non-invasive prenatal diagnosis.</p><p><b>METHODS</b>Maternal DNA extracted from plasma samples of 10 pregnant women at early pregnancy, medium pregnancy and late pregnancy and their husband's DNA isolated from whole blood samples were used to detect genotype by multiplex fluorescent PCR at nine different polymorphic short tandem repeat(STR) loci.</p><p><b>RESULTS</b>Fetus-specific alleles were found in maternal plasma samples studied. By the application of these polymorphic short repeat sequences, every pregnant women/husband pair was informative in at least three of nine loci. Paternally inherited fetal alleles were detected in 23 of 30 plasma samples. They are 6/10 cases in early pregnancy, 8/10 cases in middle pregnancy and 9/10 cases in late pregnancy respectively.</p><p><b>CONCLUSION</b>Fluorescent multiplex PCR can be used for amplification of male and female fetal STRs in maternal plasma to obtain genetic information, which may have implication for non-invasive prenatal diagnosis of certain hereditary diseases independent of the fetal sex.</p>