Progesterone action in the myometrium and decidua in preterm birth

Progesterone is central to many reproductive processes and is critical in regulating the menstrual cycle and maintaining pregnancy. We discuss here similarities in the molecular mechanisms that regulate the process of decidualisation in endometrial stromal cells and uterine quiescence in myometrial smooth muscle cells. We discuss recent evidence that the decidua may be an important mediator of progesterone actions in the onset of labor in mammalian species lacking progesterone withdrawal. These observations have relevance to recent clinical observations of the effect of progesterone administration in the prevention of preterm labor. We suggest that further research is required to understand the role of progesterone in maintaining the decidua in late pregnancy and particular focus should be given to the mechanisms that increase prostaglandin production in the uterus at term.