Progesterone is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the major progestogen in the body. Progesterone is a female sex hormone. It's produced mainly in the ovaries following ovulation each month. It's a crucial part of the menstrual cycle and maintenance of pregnancy. ... After you ovulate each month, progesterone helps thicken the lining of the uterus to prepare for a fertilized egg.