When talking about non-invasive prenatal testing, it should be noted that the concept of fetal DNA is erroneous, as the material being analysed is placental DNA. However, it is accepted to use the terms placental DNA, fetal DNA and fetal fraction as synonyms. During pregnancy, the mother’s bloodstream contains a mixture of cell-free DNA from her cells and placental cells. The placenta is the tissue in the uterus that links the foetus to the mother’s blood supply. These cells are shed into the mother’s bloodstream throughout pregnancy. The DNA of placental cells is usually identical to that of the foetus. Analysis of cell-free DNA from the placenta offers the opportunity for early detection of certain genetic abnormalities without harming the foetus.