The test method of the PrenaTest® is based on the analysis of cell-free DNA (cfDNA) in the pregnant woman’s blood. The cfDNA is present in fragments and freely circulates in the maternal blood. In addition to maternal cfDNA, it also contains approx. 2–40% (on average approx. 10%) cell-free fetal DNA (cffDNA). The cffDNA essentially comes from the cytotrophoblast, that is, from placental cells of the growing embryo and is thus of extra-embryonic origin (Fig. 1). It develops through apoptosis and necrosis of the trophoblast cells and is continually excreted into the pregnant woman’s bloodstream. The lifespan of the DNA fragments is about two hours. Within a few hours after birth of the child, the cffDNA is no longer detectable in the mother’s blood. With the PrenaTest®, the cffDNA in the maternal blood is used to determine whether there is a chromosomal imbalance for a particular chromosome to thus determine a corresponding chromosomal disorder in the unborn child. Prenatal tests based on this method are known as non-invasive prenatal testing (NIPT).