What is ovulation?

A woman’s reproductive system revolves around the monthly task of ovulation—releasing an egg ripe for fertilization. This is true from the time that women begin menstruating until menopause.

Phases of the Menstrual Cycle

  • The follicular phase of the menstrual cycle begins the day your period starts and lasts for about 12–14 days, until you ovulate or release the egg.
  • During the early part of this stage of the cycle, the female sex hormones estrogen and progesterone are at their lowest levels.
  • Another hormone, ­follicle-stimulating hormone, is produced, which turns on estrogen production. This prepares the ovary to respond to a surge of a second pituitary hormone called luteinizing hormone. The mid-cycle surge of luteinizing hormone causes the ovary to release an egg midway through the cycle.
  • After egg release, the luteal phase takes over. Luteinizing hormone triggers the ovary to produce estrogen and progesterone. These hormones cause the lining of the uterus to thicken, in preparation for a possible pregnancy.
  • If fertilization does not occur, the ovary stops making estrogen and progesterone. The sudden loss of estrogen and progesterone cause the shedding of the uterine lining, and menstruation occurs.
Dr. Mehmet Oz, MD
Cardiology (Cardiovascular Disease)
In a sexually mature female, the ovaries take turns each month releasing a single mature egg from a follicle, for possible fertilization.  This process is called ovulation.  Watch the animation to learn more about the ovaries.


Ovulation occurs when a woman's ovary releases an egg (ovum) as part of the monthly menstrual cycle. Ovulation usually happens at around day 14 of a typical 28-day cycle. The egg matures inside a follicle, or fluid-filled cyst, in one of the ovaries (two small glands found in the pelvic area). The follicle bursts and releases the egg, which is then carried into the fallopian tube that leads to the uterus (womb). If sperm are in the woman's reproductive tract, the egg may be fertilized while in the tube.

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