Anovulation (no ovulation) is a disorder in which eggs do not develop properly, or are not released from the follicles of the ovaries. Women who have this disorder may not menstruate for several months. Others may menstruate even though they are not ovulating. Although anovulation may result from hormonal imbalances, eating disorders, and other medical disorders, the cause is often unknown. Women athletes who exercise excessively may also stop ovulating.
Oligoovulation is a disorder in which ovulation doesn’t occur on a regular basis, and a menstrual cycle may be longer than the normal cycle of 21 to 35 days.