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An increased fetal DNA concentration in maternal plasma has been observed in placental pathological conditions associated with hypertension and preeclampsia. To confirm these data, we performed real-time quantitative PCR on the SRY gene in a group of physiological and pathological male-bearing pregnancies. In 78 physiological pregnancies, fetal DNA concentration in maternal plasma was 20.7, 13.4, 23.6, and 74.8 genome-equivalents (g.e.)/mL during the first, second, and third trimesters and at term, respectively. In 10 preeclamptic women, fetal DNA concentration ranged from 59.3 to 615.2 g.e./mL (median: 332.9). In 7 women with preeclampsia and IUGR (intrauterine growth retardation), fetal DNA ranged from 96.5 to 859 g.e./mL (median: 146.8). In 4 women with IUGR and hypertension, fetal DNA ranged from 34 to 473.5 g.e./mL (median: 142.4). In 3 patients with IUGR, fetal DNA ranged from 168.6 to 519.7 g.e./mL (median: 308.1). In 2 patients with IUGR and HELLP (hemolysis, elevated liver enzymes, and low platelet count) syndrome, fetal DNA concentration ranged from 105 to 394.1 g.e./mL (median: 249.7). Four women who developed preeclampsia some weeks later showed fetal DNA levels within the physiological range. These data suggest that increased fetal DNA concentrations might represent a valuable marker of placental abnormalities and suggest that this rise may precede clinical manifestation of preeclampsia by only a few weeks.

We wanted to verify whether gestational age influences the retrieval of fetal deoxyribonucleic acid in maternal blood to identify the best period for maternal blood sampling for a future noninvasive prenatal diagnoses.We amplified 81 deoxyribonucleic acid samples extracted from the peripheral blood of 27 pregnant women (18 bearing male fetuses and 9 bearing females) by nested polymerase chain reaction of the Y-specific sequence DYS14. We obtained three blood samples (one per gestational trimester) from each woman. Statistical evaluation was assessed by the McNemar test of symmetry.Polymerase chain reaction results in male-bearing pregnancies differed significantly between the first and second trimesters and between the second and third trimesters (p0.025) in parallel with a decrease in sensitivity in the second trimester (67%) compared with the first (94%) and third trimesters (100%).The drop in sensitivity from the first to the second trimester witnesses a variable concentration of fetal cells in maternal blood, with a negative balance in the second trimester. Therefore, to achieve an adequate polymerase chain reaction accuracy, the choice of gestational age is relevant and the first trimester seems to be more suitable than the second trimester.

One potential noninvasive approach for antenatal diagnosis is the use of fetal cells in maternal circulation as a source of fetal DNA (1). To date, fetal DNA has been extracted from maternal nucleated blood cells and amplified by nested PCR of Y-chromosome sequences from male fetuses (2)(3). A recent study (4) demonstrated the presence of fetal DNA in maternal plasma. After a single PCR with a high number of cycles, detection of fetal DNA was possible in 24 (80%) of the 30 maternal plasma samples, using 10 μL of boiled plasma (4). When DNA extracted from a similar volume of whole blood was used, only 17% of the samples gave a Y-positive signal, suggesting an enrichment of fetal DNA in plasma compared with whole blood cells (4). The mechanism responsible for fetal DNA release in maternal circulation is unclear. It has been postulated that fetal cell lysis after physical and immunological damage, as well as developmentally regulated apoptosis of certain fetal tissues, may be responsible for this phenomenon (5). Furthermore, the release and clearance of fetal DNA from maternal plasma may be influenced by pathophysiological factors that are still to be determined. The efficacy of the single PCR protocol on maternal plasma DNA has not yet been compared to established methodologies of nested amplification of DNA prepared from intact cells. The present work compares single PCR on plasma DNA with nested PCR on DNA extracted from plasma or nucleated blood cells. We collected 27 maternal blood samples at gestational ages ranging from the 7th to the 32nd weeks (16 male- and 11 female-bearing pregnancies). Nine, 14, and 4 samples were from the first (7–12 weeks), second (14–20 weeks), and third (27–32 weeks) trimesters. Fetal gender was unknown at the time of sampling and analysis and was verified …