Fetal cells in the mother: from genetic diagnosis to diseases associated with fetal cell microchimerism.

Fetal cells circulate in the blood of pregnant women. When the gestation is normal, fetal cells are low in number. Complications of pregnancy, such as pre-eclampsia, or fetal cytogenetic abnormalities, such as Down's syndrome, increase fetomaternal transfusion. The isolation of fetal cells from maternal blood is currently under active investigation as a non-invasive method for prenatal diagnosis. The fetal cells that are most commonly used for non-invasive genetic diagnosis, the nucleated erythrocyte and the trophoblast, are highly differentiated and do not persist post-partum. In the context of studying fetal cells in maternal blood it was discovered that fetal progenitor cells originating from a prior pregnancy could also be detected. This led to the appreciation that unlike fetal DNA in plasma, which is cleared almost immediately following delivery, fetal cells persist for decades post-partum. Following pregnancy, labor, and delivery, a woman becomes a chimera. Transfused fetal stem and progenitor cells appear to be capable of further differentiation and migration to maternal organs. A further research agenda is needed to explore the newly appreciated phenomenon of bi-directional fetomaternal cell trafficking. Any consideration of the fetus as a patient must also consider the fetus as a potential source of therapeutic stem cells for the mother.