Fetal DNA in maternal plasma as a screening variable for preeclampsia. A preliminary nonparametric analysis of detection rate in low-risk nonsymptomatic patients.

OBJECTIVE: Our objective was to examine whether plasma fetal DNA can be used as a screening variable in those women who developed preeclampsia but without any clinical symptom at the time of blood draw. METHODS: Fetal DNA was extracted from 1.5-mL plasma samples, and the DYS14 gene was analyzed by real-time quantitative polymerase chain reaction. Plasma collected and frozen from six women were each paired with five matched control samples of identical specimen type from gravid women carrying a presumed normal male fetus. Matched rank-sum analysis and nonparametric receiver operating characteristic (ROC) curves analysis of estimated multiples of median (MoM) were used for calculating detection rate (DR) and false-positive rate (FPR). RESULTS: The mean observed rank of 5.08 in the cases was significantly higher than the expected 3.18 (p-value = 0.013). Pregnancies that will develop a preeclampsia exhibit 2.39-fold higher levels of maternal plasma cell-free fetal DNA compared to matched controls. DR was 33 and 50% at an FPR of 5 and 10% respectively. CONCLUSIONS: The estimated DR allows to consider fetal DNA as a potential variable to predict preeclampsia in a low-risk population. Further studies will be addressed to calculate a parametric statistical algorithm and to estimate a proper posterior risk of the disease by means of fetal DNA alone or combined with other markers.

Evaluation of bidirectional transfer of plasma DNA through placenta.

To clarify the origin of cell-free fetal DNA in maternal plasma, we analyzed bidirectional transfer of plasma DNA between fetus and mother. We analyzed maternal and fetal plasma DNA obtained from 15 pregnant women at the time of Cesarean section. The subjects were five patients with preeclampsia and 10 gestational-age-matched normal controls. DNA was extracted from 1.5-ml plasma samples and the cellular fraction of maternal and umbilical blood. Seven polymorphic marker genes were analyzed. The relative concentration of fetal DNA in maternal plasma and maternal DNA in cord blood were evaluated. The relative concentration of maternal DNA in fetal circulation (median, 0.9%; range, 0.2-8.4%) was significantly lower than that of fetal DNA in maternal blood (14.3%, 2.3-64%), with P=0.007. The relative concentration of maternal DNA in fetal blood was not affected by preeclampsia. These findings indicate that cell-free DNA is unequally transferred through the placenta. The structural characteristics of the placenta suggest that the majority of cell-free fetal DNA in maternal plasma is derived from villous trophoblasts.