Abstract
Decidualization is a dynamic, multistep process that results in the differentiation of elongated endometrial stromal cells into round, epithelioid-like decidual cells in response to increasing progesterone levels. Throughout pregnancy, decidual stromal cells play an important role by creating a tolerant microenvironment, the decidua, to suppress the maternal immune response and prevent rejection of the allogeneic fetus. Decidualization is considered significant not only in the establishment and maintenance of pregnancy, prevention of early losses, and modulation of the immune response but also in the control of the onset of labor, regulation of trophoblast invasion, and embryo selection. Decidual cells have immunomodulatory properties in relation to cells of innate and adaptive immunity. Pregnancy maintenance requires selective elimination of proinflammatory senescent decidual cells by activated uterine natural killer cells. Data on various populations of decidualizing endometrial stromal cells revealed subtypes with different functional characteristics, namely, predecidual, decidual, transitional, and senescent subpopulations. An increase in the number of the latter with a proinflammatory phenotype leads to miscarriages. This paper analyzes the literature data on decidualization and its role in the genesis of miscarriage and highlights the contribution of decidual stromal cells to the microenvironment and their direct or indirect influence on the recruitment, distribution, and function of immune cells, extracellular matrix remodeling, and placenta formation.