The Effect of Pregnancy on Production of Maternal Endogenous Hematopoietic Stem Cells.

Fetal microchimerism refers to the presence of fetal cells in maternal blood and tissues during pregnancy. This microchimerism may result from trafficking of fetal and maternal blood across the placenta during pregnancy. Physiological changes in the maternal blood cellular milieu are also recognized during pregnancy and in the early post partum period. Earlier studies showed that maternal blood contains CD34(+) hematopoietic stem cells (HSCs) that bear paternal genetic markers or male phenotype, suggesting that these cells circulated to the mother from male fetuses during pregnancy. Other studies showed that these maternal HSCs have significantly lower expansion potential than their fetal counterparts. We have recently shown increased percentages of CD34(+) HSCs in peripheral blood of pregnant and parous women. Herein, we hypothesize that pregnancy stimulates the production of endogenous CD34(+) HSCs of maternal origin, a phenomenon which potentially could favor post partum regenerative capacity.