Myeloid-derived suppressor cells (MDSCs) are a cell population involved in the regulation of immune response by means by inhibiting it in pathologies, as well as during pregnancy. This review summarizes the available data on the effect of MDSCs on different components of innate and adaptive immunity, taking into account the different ways in which their immunosuppressive functions are carried out. Analysis of current studies on the mechanisms of suppression of the MDSC immune response are presented, and an assessment is given of the role of MDSCs in maintaince of immune tolerance during pregnancy. Data on MDSCs in various pathological conditions during pregnancy and the content of MDSCs in umbilical-cord blood were examined, and the relationship between these cells and the immune status was reviewed.