The Pre-Ovulatory Phase is the phase between bleeding and ovulation and tends to be more variable than the second half of the menstual cycle. Although about 20 follicles begin developing each menstrual cycle due to FSH release only one follicle reaches full maturity. As the follicles develop they release estrogen, which in turn feedbacks to the brain and causes the pituitary gland to cease the production of FSH. The follicle that has matured the most - survives and continues to grow until it is ready for ovulation. The other less mature follicles stop growing (and some even die).