Progesterone: The hormone produced by the corpus luteum in the ovary after ovulation. Progesterone supports the growth of the endometrium. It also causes BBT to rise, and cervical fluid to dry up after ovulation. If fertilization occurs, the body will continue to produce progesterone throughout early pregnancy. If fertilization does not occur, the corpus luteum stops producing progesterone 12-16 days after ovulation, and the endometrium is shed during menstruation.