In medicine, anovulation is absence of ovulation when it would be normally expected (in a postmenarchal, premenopausal woman). For most women, alteration of menstrual periods is the principal indication of chronic anovulation. Ovulatory menstrual periods tend to be regular and predictable in terms of cycle length, duration and heaviness of bleeding, and other symptoms. Chronic anovulation is a common cause of infertility.