Persistant corpus luteum cyst of pregnancy: sonographic evaluation of cause of third trimester bleeding.

Corpus luteum cysts are frequently observed in pregnant patients evaluated with diagnostic ultrasound. They are usually regarded as incidental findings because of their limited size and usual pattern of regression by ten weeks. The presence and persistence of larger corpus luteum cysts or other extrauterine masses may complicate pregnancy. A case of a large persistent corpus luteum cyst associated with third trimester bleeding is presented.