In gynecology, a pelvic ultrasound uses inaudible sound waves to create an image of a woman’s bladder, uterus, fallopian tubes, cervix and ovaries.
The scientific principle for ultrasounds is similar to that of sonar sound technology used by boats and submarines. The sound waves in ultrasounds are at frequencies from 2 million to 10 million cycles per second, or Hertz. The limit of human hearing is 20,000 cycles.
These frequencies create echoes in the body’s tissue, which are returned and transmitted into images by the sonography equipment.
Ultrasounds take clear pictures of human organs that are solid and uniform or are fluid filled (such as the bladder). Bones and air-filled organs (such as intestines) are not clear on ultrasounds and may block other organs from clear view.
Ultrasound equipment is usually mounted on a rolling cart that holds a computer, a monitor screen and a hand-held device called a transducer. During use, a doctor, nurse or technician called a sonographer holds the transducer on different areas of the patient and then watches as still images appear instantly on the monitor.
Ultrasounds can help identify abnormalities such as ovarian cysts and uterine fibroids. They can also help:
In transabdominal ultrasounds, a patient lies on her back on an examination table and a water-based gel is applied to one area of the body. This clear gel allows the transducer to make secure contact and eliminate air pockets, permitting the sound waves to pass unobstructed into the body. The ultrasound operator presses the transducer against the skin and may also sweep over certain areas of interest.
A transvaginal ultrasound measures the shape and size of the uterus. In this procedure, a patient usually lies face-up (sometimes with feet in stirrups), and a probe is inserted into the vagina two or three inches. This kind of ultrasound can provide a detailed image of the uterus, measure the thickness of the endometrium, and help determine overall uterine health.
A hysterosonogram is a type of transvaginal ultrasound in which saline is forced into the uterus through a thin tube called a catheter. The saline allows the technician, nurse or doctor better views of the uterus, often revealing small lesions that might otherwise go undetected.
Transvaginal ultrasounds are often more useful for women who are overweight, undergoing treatment for infertility, have a lot of gas in the intestines, or experience extreme discomfort with full bladders.
To prepare for a transabdominal ultrasound, a patient must drink four to six glasses of water about an hour before the ultrasound. This fills the bladder and gives a better picture.
Conversely, for a transvaginal ultrasound, the patient must empty her bladder in advance.
Before a pelvic ultrasound, the patient usually takes off most or all clothing and jewelry below the waist and wears a gown.
During the process, ultrasounds cause no pain or discomfort other than the sensation of cold gel and instrumentation against skin or the insertion of a small probe in the vagina. In the case of hysterosonograms, the woman may feel discomfort or a full sensation from the saline solution.
It is very important for the patient to lie still during an ultrasound. Often the patient is asked to take and hold a breath for several seconds during the procedure. Sometimes the patient will wait while a doctor looks at and interprets the images. Occasionally the doctor may order more pictures.
After the ultrasound, the patient can wash the gel from her skin and get dressed.