Amniotic fluid stem cells and fetal cell microchimerism.

Fetal cells (and cell-free, fetal DNA used for non-invasive prenatal diagnosis) are known to exist in the circulation of pregnant women. These cells exhibit stem cell properties when they differentiate at the site of injured maternal tissue, but the origin of these fetal, natural, and probably reparative cells is unknown. During pregnancy, mobilized pluripotent fetal stem cells of yet unidentified in vivo significance float in the amniotic fluid, and we argue that circulating fetal cells and the pluripotent amniotic fluid cells might share a common origin.