After ovulation, the
ruptured ovarian follicle becomes the
corpus luteum. While the ovarian
follicles produced estrogen, the corpus
luteum produce both estrogen and
Progesterone is required for
maintenance of the endometrial lining of
the uterus where the blastocyst is
If the released egg is not fertilized, the
corpus luteum regress, and the production of
progesterone drops. The uterine lining is sloughed off, completing the monthly uterine cycle. Following the menstrual period, the ovarian and uterine cycles begin anew, with the development of an ovarian follicle, and the preparation of the uterus for blastocyst implantation.
Oral contraceptives normally contain progesterone, or progesterone in combination with other estrogens. By maintaining a slightly elevated level of progesterone via oral contraceptives (or injectible contraceptives), the signals from the brain to the ovaries to initiate the ovarian cycle that lead to follicle maturation are repressed, and ovulation does not occur.