Definition of Ovarian cysts:

An ovarian cyst is a sac filled with fluid that forms on or inside of an ovary.

This article is about cysts that form during your monthly menstrual cycle, called functional cysts. Functional cysts are not the same as cysts caused by cancer or other diseases.

For more information about other causes of cysts on or near the ovaries, see also:

• Dermoid cyst
• Ectopic pregnancy
• Endometriosis
• Ovarian cancer
• Polycystic ovary syndrome

Causes, incidence, and risk factors:

Each month during your menstrual cycle, a follicle (where the egg is developing) grows on your ovary. Most months, an egg is released from this follicle (called ovulation). If the follicle fails to break open and release an egg, the fluid stays in the follicle and forms a cyst.This is called a follicular cyst.

Another type of cyst, called a corpus luteum cyst, occurs after an egg has been released from a follicle. These often contain a small amount of blood.

Ovarian cysts are somewhat common, and are more common during a woman's childbearing years (from puberty to menopause). Ovarian cysts are less common after menopause.

No known risk factors have been found.

Functional ovarian cysts are not the same as ovarian tumors (including ovarian cancer) or cysts due to hormone-related conditions such as polycystic ovary disease.

Taking fertility drugs can cause a condition called ovarian hyperstimulation, in which multiple large cysts are formed on the ovaries. These usually go away after a woman's period, or after a pregnancy.