A Dr. Elena Yanushpolsky, MD, OBGYN (Obstetrics & Gynecology), answered on behalf of Brigham and Women's Hospital. Progesterone is a hormone that is secreted by the ovary after ovulation. During the first two weeks of the menstrual cycle, the growing egg is surrounded by granulosa cell.uring that time, up until ovulation, granulose cells mainly secrete the hormone estrogen. Once ovulation takes place and the egg is released from the ovary, granulosa cells change their secretion pattern and begin to secrete progesterone in addition to estrogen.