The discovery of cell-free DNA molecules in maternal plasma has opened up numerous opportunities for noninvasive prenatal testing. The advent of new digital counting technologies, including digital polymerase chain reaction and massive parallel sequencing, has provided the opportunity to quantify the cell-free DNA molecules in maternal plasma in an unprecedentedly precise manner. Powered by these technologies, prenatal testing of different kinds of hereditary conditions, ranging from monogenic diseases to chromosome aneuploidies, has been shown to be possible through the analysis of maternal plasma DNA. Discussed here are the principles of the approaches used in the noninvasive testing of different fetal conditions, with an emphasis on the impact that different digital DNA counting strategies have made on the development of these tests.
Keywords: NIPT; cell-free fetal DNA; digital PCR; massive parallel sequencing; maternal plasma.