Decídua

Decídua is a term used in anatomy and obstetrics to denote the decidua, the specialized mucous membrane that lines the uterus during pregnancy. It arises from the maternal endometrium under the influence of pregnancy hormones, particularly progesterone, and serves to support implantation and placentation.

The decidual tissue is classically described as consisting of three regions: decidua basalis, decidua capsularis, and decidua parietalis. The decidua basalis is the portion beneath the implanted embryo and forms, together with the fetal placental tissue, the maternal part of the placenta. The decidua capsularis covers the implanted embryo on the luminal side of the uterus, while the decidua parietalis (or decidua vera) lines the rest of the uterine cavity. During early placentation, the decidualized stroma contains large secretory cells that produce nutrients, growth factors, and immune-modulatory molecules to support the embryo and regulate invasion by placental tissue.

Functions of the decidua include nourishing the early embryo, facilitating proper trophoblastic invasion, and contributing to maternal–fetal immune tolerance by secreting cytokines and other signals that modulate the local immune response. It also participates in remodeling maternal spiral arteries to establish an appropriate placental blood supply.

After delivery, the decidual tissue is shed as part of the lochia. The term derives from Latin decidua, meaning “things that fall off,” reflecting its role in temporary, pregnancy-associated tissue that is shed after birth.