A menstrual cycle during which no egg (ovum) is released.
In an anovulatory menstrual cycle, a woman does not release an egg (ovum), resulting in an infertile cycle. The subsequent release of the uterine lining is known as anovulatory bleeding, rather than menstruation. This condition may happen for many reasons, all of which are linked to atypical levels of estrogen, luteinizing hormone (LH), or follicle stimulating hormone (FSH).
The first half of a normal menstrual cycle is concentrated around increasing the uterine lining (endometrium) and releasing an egg. FSH enables immature eggs housed in the ovary to develop. As these eggs mature, estrogen is released. The rise in estrogen triggers the pituitary gland to release LH rather than FSH. The LH surge causes the most mature egg to be released from its ovarian follicle. The empty follicle is now known as the corpus luteum and releases progesterone, a hormone that will be necessary to maintain a pregnancy. The subsequent series of events depend on whether the released egg is fertilized or not.
In an anovulatory cycle, there is enough estrogen to build the uterine lining, but the hormone ratios necessary for ovulation are absent. Anovulatory bleeding occurs because of a drop in estrogen or because the endometrium is no longer self-sustaining. Although the flow is irregular, a woman may not be able to tell the difference between an ovulatory versus an anovulatory cycle.
Anovulatory cycles happen to every fertile woman at some point in time; however, there are developmental periods when such cycles are more frequent. During early adolescence, anovulatory cycles are very common as the young girl’s body slowly develops its ability to regulate hormone levels and maintain predictable menstrual cycles. Anovulatory cycles also are experienced by women who are pregnant or consistently breastfeeding, as both activities suppress the release of estrogen. In later years, anovulatory cycles can precede menopause, a period when estrogen levels drop and a woman’s body is less responsive to LH and FSH.
In addition, any behavior or situation that impacts hormone levels can result in anovulatory cycles. For example, stress, illness, strenuous exercise, and travel have been linked to anovulation. Being underweight or overweight can interfere with estrogen levels and thus cause anovulatory cycles. Women who stop using a hormone-based birth control method (e.g., birth control pills) may experience anovulatory cycles as their body works to resume control of the natural feedback system that regulates hormone levels. Last, anovulatory cycles also may result from serious medical conditions, such as polycystic ovarian syndrome (PCOS) or thyroid disease.
Depending on the cause, anovulatory cycles may be a temporary or lasting condition. Most cases can be diagnosed by a health care provider and are treatable.