Ovulation and Fertility

Difficulties with the monthly ovulation cycle are common in women with fertility issues. A very long or short cycle or irregular periods could indicate a problem with ovulation. Our fertility doctors, Dr. George Koulianos and Dr. George Inge can pinpoint and treat any issues to help you achieve your goal of a healthy pregnancy.

Understanding Ovulation

The first day of an ovulation cycle is referred to as Cycle Day One. It is the first day of full-flow menstrual bleeding. At this time, each of several “resting” antral follicles in the ovary contains an immature egg. This is called the Follicular Phase.

The pituitary gland produces Follicle Stimulating Hormone (FSH), which causes one of the follicles to become dominant, to grow, and to release estradiol as the egg matures. Estradiol causes thickening of the uterine lining (also called the endometrium), which prepares it to receive a fertilized egg.

When estradiol levels are adequate and the dominant follicle is between 18-25 mm, the pituitary gland then releases a surge of Luteinizing Hormone (LH), marking the beginning of the Luteal Phase. This LH surge causes the egg to mature and to be released. It also causes the follicle to produce progesterone, which further prepares the uterine lining for pregnancy.

If there is no pregnancy, the estradiol and progesterone levels will fall, which causes the uterine lining to shed and bleed, ending the cycle.

Length of Cycles

Menstrual cycles vary in length, but are typically 21 to 35 days long. The Follicular Phase has the most variation and is generally between 7 and 21 days in length, while the Luteal Phase tends to be a consistent 14 days. Very irregular cycles, or cycles that are longer than 35 days are frequently anovulatory cycles with no egg released.


  • The pituitary gland secretes FSH to stimulate the ovary.
  • The FSH causes the egg to mature and the ovary to produce estradiol.
  • Estradiol causes the lining of the uterus (endometrium) to thicken to allow for implantation of a fertilized egg.
  • An LH surge causes the release of the egg and signals the follicle to make progesterone, also thickening the uterine lining.
  • If no fertilized egg implants, the progesterone and estradiol hormone levels fall, causing the uterine lining to shed resulting in a period.
  • The fall in hormone levels signals the pituitary gland to start the cycle all over again.

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