An ovarian cyst in which a fluid-filled sac develops from a persistent corpus luteum, the yellow pouch that remains after an egg has been released from a follicle (egg sac) in the ovary. If the egg is not fertilized, the body normally resorbs the corpus luteum. Corpus luteum cysts usually go away in a few weeks but can grow as large as 4 or more inches in diameter and can cause pain in the woman’s lower abdomen, usually on only one side. A corpus luteum cyst may cause delayed menstrual periods or bleeding between menstrual periods. If a woman develops symptoms of a corpus luteum cyst, her doctor will usually perform a pelvic examination and may order tests such as ultrasound scanning, to rule out conditions such as cancer, ectopic pregnancy, or Other noncancerous ovarian growths.