Contraceptive pills containing estradiol or estradiol plus progesterone

Slightly elevated levels of estradiol or estradiol and progesterone inhibit both GnRH at the hypothalamus and the release of FSH and LH from the pituitary. Without FSH, primordial follicles do not initiate development, and the endogenous levels of estrogen remain low. An LH surge is necessary for ovulation to occur, and the LH surge is triggered by the peaking of estradiol. If the level of estradiol is not allowed to rise above the critical level, the LH surge will not occur and ovulation will not occur, even if a follicle managed to develop to a stage at which it could ovulate. Any mature follicles would ultimately degenerate, and no new follicles would mature to take their place. Although the ovarian cycle is interrupted, the level of hormones is still adequate to regulate a normal menstrual cycle.