Fetomaternal cellular and plasma DNA trafficking: the Yin and the Yang

In human pregnancy, multiple lines of evidence have indicated that there is trafficking of nucleated cells and cell-free DNA between the mother and fetus. Diagnostically, fetal cells in maternal blood and fetal DNA in maternal plasma offer a noninvasive source of fetal material for prenatal diagnosis. Through the developments of methods for fetal cell isolation and fetal DNA detection, many fetal genetic characteristics and chromosomal abnormalities have been detected from maternal blood. Large-scale clinical trials have been initiated that will facilitate the eventual application of these technologies. The presence of large quantities of cell-free fetal DNA in maternal plasma challenges the conventional belief that the fetal and maternal circulations are separate entities. In addition, the recent demonstration of the persistence of fetal cells following delivery also opens up a new field of investigation and raises new physiologic and pathogenic implications. Like the Yin and Yang in Chinese mythology, we believe that fetal cells and fetal DNA transfer are closely related and should be studied and applied in a synergistic manner.