decidualization

Decidualization is the transformation of endometrial stromal cells into specialized decidual cells in the lining of the uterus, driven primarily by progesterone after ovulation. This process prepares the endometrium for embryo implantation and supports early pregnancy by creating a tissue that nourishes the conceptus and modulates maternal immune responses.

Mechanistically, progesterone (often with estrogen and intracellular signaling pathways such as cAMP) induces differentiation of stromal fibroblasts into large, polygonal decidual cells rich in glycogen and lipid droplets. decidual cells secrete hormones and factors, including prolactin and IGFBP-1, along with cytokines and chemokines that regulate inflammation, promote vascular remodeling, and influence trophoblast invasion. The decidua also contributes to angiogenesis and the restructuring of spiral arteries to improve placental blood flow while helping maintain immune tolerance at the maternal–fetal interface.

Anatomically, in humans the decidua refers to the maternal portion of the placental unit and is subdivided into decidua basalis (at the implantation site), decidua capsularis (overlying the conceptus), and decidua parietalis (the remaining decidua lining the uterus). After implantation, decidua basalis forms part of the placenta (the decidua basalis/placental bed), while capsularis and parietalis participate in the surrounding uterine environment as pregnancy progresses.

Timing and occurrence vary among species. In humans and many primates, decidualization is a preparation for potential pregnancy and is maintained if implantation occurs; if pregnancy does not occur, the decidualized tissue degenerates and is shed during menstruation.

Clinical relevance includes associations between defective decidualization and infertility, recurrent pregnancy loss, and placental dysfunction disorders. Research into decidualization informs reproductive biology and potential therapeutic approaches to pregnancy-related conditions.