Fetal cells and cell-free fetal DNA in maternal blood: new insights into pre-eclampsia.

The examination of fetal cells, specifically erythroblasts, and cell-free fetal DNA from the blood of pregnant women is currently the subject of intense research with the aim of developing new risk-free methods for prenatal diagnosis. An unexpected finding made during these studies was that the traffic of fetal erythroblasts into the maternal peripheral circulation was enhanced in pre-eclampsia. Independent prospective studies examining samples collected in the second trimester indicated that this perturbation in fetal cell trafficking occurs early in pregnancy, well before the onset of pre-eclampsia symptoms. The quantitative analysis of cell-free fetal and maternal DNA levels indicated that these concentrations were elevated in a co-ordinate manner in manifest pre-eclampsia, and that these elevations corresponded to disease severity. On the other hand, analysis of prospectively collected samples indicated that only cell-free fetal but not maternal DNA levels were elevated before onset of symptoms in pregnancies which subsequently developed pre-eclampsia. These data support hypotheses suggesting that pre-eclampsia is a multi-step disorder, initiated by a placental lesion that occurs early in pregnancy and which subsequently leads to a systemic maternal inflammatory response and associated endothelial cell damage.