Decidualization

Micrograph showing decidualization of the endometrium due to exogenous progesterone (oral contraceptive pill). H&E stain.

Decidualization is a characteristic of the endometrium of the pregnant uterus. It is a respond of maternal cells to progesterone. However, it's important to remember that deciduazlization may be used to describe any change due to progesterone, including the eosinophilic proliferation around arterioles after ovulation.

After ovulation, in mammals, the endometrial lining becomes transformed into a secretory lining in preparation of accepting the embryo. Without implantation, the secretory lining will be absorbed (estrous cycle) or shed (menstrual cycle). With implantation the lining now termed decidua evolves further during the pregnancy. The decidua is shed during the third phase of the parturition process.