Very large ovarian cysts can indeed create discomfort. In rare cases, such cysts can also cause the ovary to twist (torsion), and the ovary can die due to loss of blood flow.
In most cases, a pelvic ultrasound will also be performed for large pelvic cysts. The appearance of the cyst by ultrasound, as well as a blood test known as "CA 125," are often helpful in determining if the cyst is more likely to be benign versus malignant. In many cases, however, a large or/and complex ovarian cyst may require surgery in order to make the diagnosis (and to remove the cyst/ovary).
Sincerely,
Robert A. Wascher, MD, FACS
www.doctorwascher.com
Author, "A Cancer Prevention Guide for the Human Race" (2010)