Issues with ovulation are a common cause of infertility

The Monthly Ovulation Cycle

Issues with ovulation are a common cause of infertility. Irregular periods, or a very long or short cycle, may indicate a cause for concern. Your physician can help you identify and correct ovulation issues, and help put you on the path to realizing your dream of having a family.

The Ovulation Cycle


At the beginning of each cycle (first day of full-flow bleeding = day 1), there are several “resting” antral follicles present in the ovary, each containing an immature egg. Under the influence of FSH (follicle stimulating hormone) from the pituitary gland, one of these follicles becomes dominant and begins to grow and release estradiol as the egg matures. Estradiol causes the uterine lining (endometrium) to thicken, preparing it for pregnancy.


Once the follicle reaches a certain size, usually 18–25 mm, and the estradiol levels are adequate, the pituitary gland releases the luteinizing hormone (LH surge) which results in 1) final maturation of the egg, 2) release of the egg, and 3) progesterone production from the follicle, further preparing the uterine lining to receive the fertilized egg.


The LH surge (detected by a urine ovulation predictor kit, or “OPK”) signals ovulation and the beginning of the luteal phase (the time from ovulation to the next period). In the absence of pregnancy, estradiol and progesterone levels eventually fall, allowing the uterine lining to shed and bleed, resulting in the next period.


The duration of a menstrual cycle varies, typically 21 to 35 days. Most of the variation is due to the follicular phase which may be anywhere from 7 to 21 days. The luteal phase is more consistent at approximately 14 days. Cycles that are very irregular or longer than 35 days are often “anovulatory cycles” meaning that no egg is released.


  • Hormone signals (FSH) from the pituitary gland stimulate the ovary.
  • In response to FSH, an egg matures and the ovary produces estrogen. Estrogen, in turn, stimulates the lining of the uterus (endometrium) to thicken in preparation for the implantation of a fertilized egg.
  • The LH surge causes the egg to be released and stimulates the ovary to make progesterone.
  • In the absence of pregnancy, the ovarian hormone levels fall signaling the uterine lining to shed and a withdrawal bleed (period) to occur.
  • The fall in ovarian hormones results in an increase in the pituitary hormone signals, starting the cycle all over again.