Twenty-two fetuses were female; 30 were male. Four male fetuses were aneuploid, including one case each of trisomies 13, 18, and 21 and one case of mosaicism (92, XXYY/46, XY ). The other 26 male fetuses were euploid. Due to the small number of aneuploid cases, these fetuses were not analyzed separately from the euploid cases. DYS1 amplification was undetectable in all female fetuses (specificity = 100%). The sensitivity of DYS1 detection when the fetus was male was 100%. In male fetuses, the mean concentration of the DYS1 sequence pre CVS was 13.1 genome equivalents (GE)/mL (range: 1.2 to 122 GE/mL) and 12.9 GE/mL (range: 1.1 to 67.3 GE/mL) post CVS ().
Effects of variables on cell-free DNA quantities in pre- and post-CVS maternal plasma samples
Overall, there were no statistically significant differences in absolute quantities of total (GAPDH) DNA pre-and post-procedure, nor were there statistically significant effects of any of the variables that were studied (). Similarly, there were no overall statistically significant differences in the level of fetal (DYS1) DNA levels between paired samples (). However, there were differences in the number of patients with relative increases or decreases in cell-free DNA relative to baseline (i.e. pre-procedure) levels following CVS, as well as differences in the magnitude of these changes. For fetal DNA, there were 20 (67%) women who had an increase in DYS1 following the procedure, compared to 10 (33%) who had a decrease. The greatest percentage increase in fetal DNA was 907.1%, while the greatest decrease was 77.4%. The overall median percent change of DYS1 was 26.6%. There were no obvious trends among the aneuploidy cases that were analyzed. In addition, while there were only four women who showed a decrease of greater than 50% in fetal DNA, 11 women had increases of greater than 50%.
For total DNA, the results with respect to percentage change were similar to those of fetal DNA. There were 18 (60%) women who exhibited an increase in GAPDH following the procedure, compared to 12 (40%) who showed a decrease. The greatest percentage increase in total DNA was 368.3%, while the greatest decrease was 72.1%. The overall median percent change for GAPDH was 10.3%. There were three women who showed a decrease of greater than 50% in total DNA, while seven women had an increase of greater than 50%. Interestingly, the three women who had the greatest percentage increase in fetal DNA also had the greatest percentage increase in total DNA.
There was a trend toward an inverse association between post-procedure fetal DNA levels and gestational age (p=0.053) resulting, on average, in 23% lower post-procedure levels for each additional week of gestation after the adjustment for pre-procedure levels. No association of sample weight, placental location (i.e. anterior vs. posterior), or individual operator experience with changes in DNA levels with regard to the procedure were detected.