Accuracy of Fetal Gender Determination by Analysis of DNA in Maternal Plasma

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Abstract
In 1997, Lo et al. ( 1) first described the presence of fetal DNA in maternal plasma and serum. Cell-free DNA offered a new source of fetal genetic material for noninvasive prenatal diagnosis. They developed a real-time, quantitative PCR assay to measure the concentration of fetal DNA and analyzed SRY, a single-copy Y-chromosome-specific sequence, to quantify the number of genome-equivalents per milliliter of blood when a woman carries a male fetus ( 2). The results revealed that the concentrations of fetal DNA in maternal plasma DNA during the first and third trimesters were 3.4% and 6.2%, respectively. They estimated a mean of 25.4 copies of fetal DNA circulates per milliliter of maternal plasma samples during early pregnancy. They also demonstrated that after delivery, cell-free fetal DNA is cleared very rapidly from the maternal circulation, with a half-life in the order of minutes ( 3). Thus, the relatively high concentration of fetal cell-free DNA suggests that extensive and time-consuming fetal DNA enrichment procedures would not be necessary when using fetal DNA from maternal plasma for diagnostic purposes.