Introduction: Circulating fetal extravillous trophoblasts may offer a superior alternative to cell-free fetal DNA for noninvasive prenatal testing. Cells of fetal origin are a pure source of fetal genome; hence, unlike the cell-free noninvasive prenatal test, the fetal cell-based noninvasive prenatal test is not expected to be affected by maternal DNA. However, circulating fetal cells from previous pregnancies may lead to confounding results. Material and methods: To study whether fetal trophoblast cells persist in maternal cir- culation postpartum, blood samples were collected from 11 women who had given birth to a boy, with blood sampling at 1-3 days (W0), 4-5 weeks (W4-5), around 8 weeks (W8) and around 12 weeks (W12) postpartum.
The existence of fetal extravillous trophoblasts was verified either by X and Y chromosome fluorescence in situ hybridiza- tion analysis or by short tandem repeat analysis. To exclude technological bias in isolat- ing fetal cells, blood samples were also collected from 10 pregnant women between a gestational age of 10 and 14 weeks, the optimal time frame for cell-based noninvasive prenatal test sampling. All the samples were processed according to protocols estab- lished by ARCEDI Biotech for fetal extravillous trophoblast enrichment and isolation.
Results: Fetal extravillous trophoblasts were found in all the 10 samples from pregnant women between a gestational age of 10 and 14 weeks. However, only 4 of 11 blood sam- ples taken from women at 1-3 days postpartum rendered fetal extravillous trophoblasts, and only 2 of 11 samples rendered fetal extravillous trophoblasts at 4 weeks postpartum. Conclusions: In this preliminary dataset on few pregnancies, none of the samples rendered any fetal cells at or after 8 weeks postpartum, showing that cell-based non- invasive prenatal testing based on fetal extravillous trophoblasts is unlikely to be influenced by circulating cells from previous pregnancies.