For ovulation to occur, a series of synchronized messages between the pituitary gland (which is located at the base of the brain) and a healthy ovary must take place. Approximately 25% of all women with infertility have an abnormality with ovulation. Irregular cycles (<21 days or >35 days), abnormal bleeding, or a complete cessation in menses suggest an ovulatory disorder.
Ovulatory disturbances can be caused by any process which may disrupt the messages between the brain and the ovary, which can include polycystic ovary syndrome (PCOS), medications, rapid weight gain or loss, thyroid dysfunction, elevations in the milk hormone, prolactin, and chronic medical illnesses. Occasionally, no cause for anovulation may be identified, which is called idiopathic anovulation.