Timing of Decidual Changes in Endometrium

Decidualization occurs during pregnancy in mammalian species with invasive implantation of the blastocyst. In humans, unlike other species, the process of decidualization is initiated in the second half of the menstrual cycle even in the absence of pregnancy. One of the most obvious features of decudualization is the transformation of stromal cells in the endometrium from a proliferative to a secretory phenotype. The main secretory products include prolactin (PRL) and insulin-like growth factor binding protein-1 (GFBP-1). Decidualization begins in the vicinity of the spiral arteries of the endometrium as early as day 23 of the menstrual cycle, triggered by the rise in cAMP and progesterone. Spontaneous decidualization, or decidualization in the absence of pregnancy, has also been reported in the chimpanzee (Grahm, 1981).

Decidualization during pregnancy is very extensive in humans and affects all regions of the uterus.