A sonohysterogram is an imaging test that uses saline (sterile salt water) and ultrasound to get a detailed look at the inside of your uterus. It’s also called a saline infusion sonogram or SIS. The procedure takes about 15 to 30 minutes, requires no anesthesia, and is done in a doctor’s office. If your provider has recommended one, it’s typically because a standard ultrasound didn’t give a clear enough picture of your uterine lining.
How the Procedure Works
A sonohysterogram starts much like a routine pelvic exam. You’ll lie on an exam table and your provider will insert a speculum. A thin, flexible catheter is then threaded through your cervix into the uterus. Once the catheter is in place, the speculum is removed and a transvaginal ultrasound probe is inserted.
Sterile saline flows through the catheter and gently fills your uterine cavity. This fluid acts like a contrast agent: it expands the walls of the uterus and creates a clear boundary between the uterine lining and any growths or irregularities inside. The ultrasound probe captures real-time images as the saline fills the space, giving your provider a much sharper view than a standard ultrasound alone could offer.
Why Your Provider Ordered One
The most common reason for a sonohysterogram is abnormal uterine bleeding, whether that means unusually heavy periods, bleeding between periods, or postmenopausal bleeding. The test is particularly good at identifying structural problems inside the uterus, including:
- Endometrial polyps: small growths on the uterine lining
- Submucosal fibroids: noncancerous growths that push into the uterine cavity
- Uterine adhesions: bands of scar tissue inside the uterus
- Endometrial hyperplasia: abnormal thickening of the uterine lining
It’s also frequently used during fertility evaluations. If you’ve had difficulty getting pregnant or have experienced recurrent miscarriages, a sonohysterogram can reveal whether the shape of your uterine cavity or an internal growth might be contributing.
How Accurate Is It?
Sonohysterograms are highly reliable. Studies comparing the procedure to hysteroscopy (a more invasive test where a camera is inserted directly into the uterus) have found comparable accuracy. For detecting submucosal fibroids, the test has a sensitivity of 90% and specificity of 98%, meaning it catches the vast majority of fibroids and rarely flags something that isn’t there. For endometrial polyps, sensitivity is about 88% and specificity is 91%. For endometrial hyperplasia, sensitivity reaches 100% with 93% specificity.
These numbers make the sonohysterogram one of the most dependable noninvasive tools for evaluating the uterine cavity. It’s considered more reliable than a standard hysterosalpingogram (HSG) for identifying problems inside the uterus, though HSG remains the preferred test when the goal is to check whether the fallopian tubes are open, since the sonohysterogram doesn’t evaluate the tubes.
When It’s Scheduled
Timing matters. The test is typically scheduled during the first 10 days of your menstrual cycle, after your period has mostly stopped but before ovulation. This window ensures the uterine lining is thin, making it easier to spot abnormalities against the saline. A study comparing results from different cycle phases found a 27% false-positive rate when the procedure was done in the second half of the cycle, compared to zero false positives when done in the first 10 days. A thicker lining later in the cycle can mimic polyps or other growths, leading to unnecessary follow-up.
If you’re no longer menstruating, the test can be scheduled at any time.
What It Feels Like
Most people describe the experience as mildly uncomfortable rather than painful. You’ll likely feel cramping when the catheter passes through your cervix and a sensation of pressure as the saline fills your uterus. The discomfort is similar to menstrual cramps and is usually brief, lasting only while the saline is being infused and the images are captured.
Pain tolerance varies. Some people find the procedure causes only minor discomfort, while others experience moderate cramping. Taking an over-the-counter pain reliever like ibuprofen or acetaminophen about an hour before your appointment can help take the edge off. No sedation or numbing is typically needed.
After the Test
You can return to your normal activities right away. Some light spotting and watery discharge are normal in the hours following the procedure, since the saline drains out on its own. Wearing a pad (not a tampon) for the rest of the day is a practical choice. Mild cramping may linger but generally resolves quickly, and over-the-counter pain relievers are usually enough to manage it.
Your provider may be able to discuss preliminary findings with you immediately after the test, since the images are captured in real time. In some cases, a more detailed review happens at a follow-up appointment, particularly if the images need to be compared with other test results or if a biopsy was taken at the same time.
Sonohysterogram vs. HSG
These two tests are easy to confuse, but they evaluate different things. A sonohysterogram uses saline and ultrasound to examine the inside of the uterus. A hysterosalpingogram (HSG) uses X-ray dye and fluoroscopy to check the uterine cavity and, more importantly, the fallopian tubes. If your provider needs to know whether your tubes are open, an HSG is the appropriate test. If the question is about what’s happening inside the uterus itself, the sonohysterogram is generally the better, more accurate choice for identifying polyps, fibroids, and other structural issues.
In fertility workups, both tests are sometimes ordered because they answer different clinical questions. They aren’t interchangeable.