Gynecology
Ultrasound is extremely useful for looking at a woman's ovaries and uterus. There can be symptoms such as pain or bloating at any age, and until some kind of imaging is done, it can be very hard to know what is causing them. Some conditions for which ultrasound can be helpful include infrequent menstruation ("periods"), infertility, ovarian cysts, movement of an IUD out of place, and even cancers of the uterus or ovaries.
Pelvic ultrasounds almost always include the use of a small instrument placed in the vagina, like a tampon ("transvaginal ultrasound"). This requires putting feet up in stirrups, like for a pelvic exam, and the position can be uncomfortable. The test itself usually does not cause any pain, just pressure (it could hurt if this area is already very painful). Your technologist will do their very best to make it comfortable for you.
If the doctor has also ordered "transabdominal ultrasound" (over the belly), you may be asked to arrive at your appointment with a very full bladder. The usual instruction is to drink 32 ounces of water an hour before you come, then do not use the bathroom. This is asked because the ultrasound pictures are much better. The full bladder acts like a window to the uterus and ovaries, and can also help push the intestines out of the way for a clearer picture.