Relative quantitation of cell-free fetal DNA in maternal plasma using autosomal DNA markers

Abstract

BackgroundCell-free fetal DNA in maternal plasma presents interest as it can possibly serve as a pregnancy associated biomarker. For its quantitation, we investigate the use of fluorescent polymerase chain reaction (PCR) amplification of short tandem repeats (STRs) in pregnancies irrespective of sex. MethodsArtificially chimeric DNA samples were prepared so as to simulate cell-free fetal DNA in maternal plasma at different proportions. The samples were tested with fluorescent PCR amplification of informative STRs and the percentage of the population simulating fetal DNA was plotted against a relative ratio of the alleles detected in each sample. The graphs were used for the quantitation of cell-free fetal DNA in 50 maternal plasma samples. ResultsDetection of at least one paternally inherited fetal STR was possible in 46/50 pregnancies leading to the estimation of the relative percentage of cell-free fetal DNA. Four pregnancies failed to reveal any fetal allele which may reflect undetectable levels (<1%) of fetal DNA. Among pregnancies fetal DNA ranged from 0 to 20% (mean value of 7%). ConclusionOur system can readily estimate the relative levels of cell-free fetal DNA in maternal circulation, normal gestations of either sex and can be exploited for estimating possible variations of this analyte between normal and pathological pregnancies.