Fetal cells and cell free fetal nucleic acids in maternal blood: new tools to study abnormal placentation?

The analysis of fetal cells, and more recently cell free fetal nucleic acids, in maternal blood has to date largely been concerned with the development of risk free methods for prenatal diagnosis. Although elevated feto-maternal cell trafficking has long been associated with preeclampsia, it has only recently been shown that this perturbation is an early event in these pregnancies, occurring well in advance of the onset of symptoms. In a separate development, analogous observations have been made concerning the levels of circulatory fetal nucleic acids in maternal plasma. Subsequent studies have shown that changes in these two parameters may also occur in other pregnancy related disorders including preterm labour, intra-uterine growth retardation, hyperemesis gravidarum or even pregnancies at high altitude. A striking finding of these examinations was that preterm labour was associated with an elevated release of cell free fetal nucleic acids but not with an increment in feto-maternal cell trafficking. This suggested that the analysis of the mechanisms regulating trans-placental cell trafficking or liberation of circulatory fetal nucleic acids may provide key insights into the fundamentally different placental lesions underlying these disorders. As such, circulatory fetal cells and nucleic acids may be viewed as new tools to study alterations in placentation.