Cell-based non-invasive prenatal testing (cbNIPT) may represent a superior alternative to cell-free fetal non-invasive prenatal testing (cffNIPT). The major argument in favor of cbNIPT is that the nucleated fetal cells contain the entire fetal genome, making it possible to perform a wider range of and more detailed genetic analyses [1–6]. Furthermore, unlike cffNIPT, cbNIPT is not significantly affected by increased maternal BMI [5, 7]. cbNIPT can be based on fetal leucocytes [8, 9] or nucleated red blood cells  found in maternal blood, but more promising and relatively well-established methods are based on extravillous trophoblasts (EVTs), circulating in maternal blood [1, 3, 4, 6, 11, 12],cell or retrieved from the cervical canal of pregnant women [13–17]. Interestingly, both methods are based on enrichment of EVTs but target different cell surface markers.
As regards to EVTs in maternal blood, ARCEDI Biotech ApS holds proprietary technology for immunomagnetic enrichment of EVTs using antibodies against the mesodermal cell surface markers CD105 and CD141, and staining of EVTs with a combination of fluorescent antibodies targeting ectodermal cytoskeletal markers [1, 3, 6]. In contrast, Trophoblast Retrieval and Isolation from the Cervix (TRIC) is based on EVTs retrieved from the cervical canal of pregnant women using cervical swabs and immunomagnetic enrichment targeting the EVT surface marker, human leukocyte antigen G (HLA-G) [13–17].
As illustrated in Fig. 1, trophoblasts originate from chorionic villi [18, 19]. Villous cytotrophoblasts proliferate in cell columns at the tip of the villi and invade the decidual stroma, where they start expressing HLA-G and mesodermal markers [18, 20]. These trophoblasts are called invasive interstitial EVTs, which may reach maternal circulation and potentially the cervical canal by different routes. HLA-G positive interstitial EVTs have been demonstrated in decidua basalis, uterine veins, arteries, and glands [13–17]. Two different routes have been proposed for EVTs reaching the cervical canal. At the margin of placenta, invasive interstitial EVTs may migrate directly into the uterine cavity or alternatively invade the uterine glands in decidua basalis and hereby reach the cervical canal during the first trimester . Furthermore, invasive EVTs migrate from decidual stroma to the uterine veins  and spiral arteries displacing the vascular endothelium, and lining the vessel wall to establish feto-maternal circulation [19, 22]. This invasion is complex and involves transition from an epithelial to mesenchymal phenotype, which allows the EVTs to invade maternal vessels [23, 24] (Fig. 1).
It is unknown whether EVTs found in the cervical canal and maternal blood express similar cell surface markers. Hence, the aim of this study was to investigate, whether the antibodies used in a cbNIPT protocol enriching EVTs from maternal blood can enrich EVTs from maternal cervical swabs.