Progesterone is a steroid hormone that plays a key role in regulating the menstrual cycle, preparing the endometrium for embryo implantation, and maintaining pregnancy.

The main source of progesterone is the corpus luteum of the ovary, which synthesizes the hormone in the second phase of the menstrual cycle under the influence of luteinizing hormone (LH). In the event of pregnancy, progesterone production is supported by human chorionic gonadotropin (hCG), and later by the placenta. Small amounts of progesterone are also synthesized in the adrenal cortex.