Fetal DNA in maternal plasma is elevated in pregnancies with aneuploid fetuses

Current non-invasive screening methods for the prenatal diagnosis of fetal aneuploidies are hampered by low sensitivities and high false positive rates. Attempts to redress this situation include the enrichment of fetal cells from maternal blood, or the use of fetal DNA in the plasma of pregnant women. By the use of real-time quantitative polymerase chain reaction (PCR) it has recently been shown that circulatory male fetal DNA in maternal plasma is elevated in pregnancies with trisomy 21 fetuses. In this independent study we confirm and extend upon these results by showing that the levels of fetal DNA are also elevated in pregnancies with other chromosomal aneuploidies (mean=185.8 genome equivalents/ml; range=62.2-471.7) when compared to pregnancies with normal male fetuses (mean=81.9 genome equivalents/ml; range=28.8-328.9), p=0.005. This elevation was greatest for fetuses with trisomy 21, whereas it was not significant for fetuses with trisomy 18, p=0.356. These data suggest that a quantitative analysis of such fetal DNA levels may serve as an additional marker for certain fetal chromosomal abnormalities, in particular for trisomy 21.