Doctors order a saline-infusion sonogram, or SIS -- also known as a sonohysterogram, SHG or water ultrasound -- as a diagnostic tool to check for problems inside the uterus. A saline-infusion sonogram is a slightly more elaborate version of a transvaginal ultrasound, which is the imaging test of choice for evaluating the female pelvic and reproductive structures because it provides valuable information but is safe in pregnancy, relatively inexpensive, and doesn't use ionizing radiation, which can have dangerous side effects. The difference between a standard transvaginal ultrasound and a sonohysterogram is that for a sonohysterogram, the uterus is filled with sterile fluid before the exam is performed; this provides significantly better images of the inside lining of the uterus than possible with ultrasound alone.
When your doctor wants to evaluate the inner lining of the uterus (medically termed the endometrium) to determine the cause of abnormal vaginal bleeding, infertility, or recurrent miscarriage, a saline-infusion sonogram adds considerably to the information obtained from regular transvaginal ultrasound. This test can identify several different problems such as uterine fibroids, endometrial polyps, retained products of conception, or congenital anomalies such as an abnormally shaped uterus.
Most medical providers check for cervical infections by doing cervical cultures several days or weeks before a saline-infusion sonogram. Your provider positions a small catheter through the cervix to fill the uterus with fluid. The catheter could theoretically spread an existing infection in the cervix to the uterus, so many providers also prescribe preventative antibiotics to be taken before and after the test. Even with the antibiotics, you can develop an infection or other complication after a saline-infusion sonogram, but the risk is very small -- less than 1 percent.
To do a saline-infusion sonogram, your medical provider first fills the uterus with sterile fluid through a sterile catheter inserted through the vagina and cervix into the uterus. He then positions the ultrasound probe inside the vagina, as this location is closest to the reproductive organs and provides the most accurate images. The probe emits sound waves at a frequency inaudible to human ears. Most transvaginal ultrasound exams take less than 10 minutes to perform; a saline-infusion sonogram typically doesn't take much longer than this.
After the Test
Although you generally don't experience much pain during a saline-infusion sonogram, you may feel some discomfort and often significant cramping. In addition to the discomfort associated with the placement of a speculum and the vaginal ultrasound probe, many women experience painful menstrual cramps when the fluid enters and distends the uterus. Taking an over-the-counter pain reliever such as ibuprofen, or even an anti-anxiety medication taken one to two hours prior to the procedure, can help minimize discomfort. After the procedure, you typically have no activity restrictions, but light cramping and bleeding commonly occur for several days following the exam. If you experience fevers, severe or persistent pains or heavy or persistent bleeding after a saline-infusion sonogram, call your medical provider to discuss your symptoms.
A saline-infusion sonogram is generally considered a good screening test for abnormalities of the endometrium. It can catch abnormalities in the uterus, but it doesn't distinguish one kind of abnormality, such as a fibroid, from another, such as a polyp. Also, while this test very reliably finds abnormalities if they do exist, false positive readings can occur, indicating that something is wrong when it isn't. If your provider interprets your test results as normal, you normally need no follow-up imaging. If the saline-infusion sonogram is abnormal, she will suggest a more definitive -- and usually more invasive -- test, such as a hysteroscopy, to verify the saline-infusion sonogram findings.