Oligomenorrhea is usually defined by menstrual intervals between 6 weeks and 6 months. This definition is, however, arbitrary and does not necessarily reflect important distinctions, indeed, they can be misleading (Hull, 1997). Transvaginal ultrasonography is likely to overcome some of the problems of the transabdominal technique because the transducer is closer to the structures of interest and not separated from them by layers of fat and muscle and the shorter distance between the transducer and pelvic organs allows the use of probes with higher ultrasound frequencies and, therefore greater power of resolution (Fox, 1999).