Fetal cells in maternal tissue following pregnancy: what are the consequences?

The presence and persistence of fetal cells in murine maternal tissue was first reported over 20 years ago, although it is only more recently that the occurrence and potential consequences of fetomaternal cell trafficking in humans have been fully appreciated. Fetal cell microchimerism is a growing field of investigation, although the data are contradictory relative to the health consequences of persistent fetal cells in maternal tissues. Understanding of the types of cells being transferred from fetus to mother, the location of these fetal cells within the various maternal tissue types, and the functionality of these cells may ultimately lead to measures to minimize or eliminate the deleterious effects of the cells, or to efforts to take advantage of the presence of these cells for therapeutic purposes. This review focuses on the origins of fetal cell microchimerism research and the different hypotheses regarding the consequences of persistent fetal cells in the mother, the various diseases that have been evaluated with respect to fetomaternal cell trafficking, the potential variables associated with the frequency, persistence and tissue distribution of fetal cells in maternal tissue, and an assessment of future direction in this innovative field of inquiry.