SIS stands for saline infusion sonohysterography, a diagnostic imaging procedure that gives your doctor a detailed look inside your uterus. It works by filling the uterine cavity with a small amount of sterile saltwater (saline) while an ultrasound captures real-time images. The saline acts like a contrast agent, expanding the walls of the uterus so abnormalities that a standard ultrasound might miss become clearly visible. The whole procedure typically takes about 15 to 30 minutes and is done in a doctor’s office, not an operating room.
Why Doctors Order an SIS
The most common reason for an SIS is abnormal uterine bleeding, which accounts for a large share of gynecology visits. When bleeding is heavier than normal, happening between periods, or occurring after menopause, a standard transvaginal ultrasound is often the first step. But if those images aren’t conclusive, SIS provides a much clearer picture of what’s happening inside the uterine lining.
SIS can detect a range of structural problems: endometrial polyps, fibroids (especially those growing into the uterine cavity), scar tissue or adhesions, uterine septums, and other congenital abnormalities. It’s also used as part of a fertility workup. If you’ve had recurrent miscarriages or difficulty conceiving, your doctor may use SIS to check whether a structural issue in the uterus could be contributing.
How SIS Compares to Other Tests
A regular transvaginal ultrasound uses a wand-shaped probe inserted into the vagina to image the uterus and ovaries. It’s useful for many things, but it doesn’t always distinguish between different types of growths inside the uterine lining. SIS dramatically improves on this. A meta-analysis comparing the two for detecting endometrial polyps in women with abnormal bleeding found that SIS had 87% sensitivity and 86% specificity, compared to just 62% sensitivity and 73% specificity for standard transvaginal ultrasound. In practical terms, SIS catches roughly a quarter more polyps that a regular ultrasound would miss.
Another test you may hear about is the HSG, or hysterosalpingogram, which uses X-ray and a contrast dye. HSG is primarily designed to check whether the fallopian tubes are open, making it more relevant in fertility evaluations focused on tubal blockage. For evaluating the uterine cavity itself, SIS is more sensitive, specific, and accurate than HSG. Hysteroscopy, where a tiny camera is inserted directly into the uterus, edges out SIS slightly in sensitivity (92% vs. 87%) but is a more invasive procedure that sometimes requires anesthesia. SIS fills a useful middle ground: more detailed than a regular ultrasound, less invasive than hysteroscopy.
What Happens During the Procedure
The process starts like a routine pelvic exam. You’ll lie on an exam table, and the clinician inserts a speculum to access your cervix. A thin, flexible catheter is then threaded through the cervical opening into the uterus. This part can cause a pinching or cramping sensation similar to what you might feel during an IUD insertion or a Pap smear, though it’s usually brief.
Once the catheter is in place, the speculum comes out and a transvaginal ultrasound wand goes in. Sterile saline flows through the catheter, gently filling and expanding the uterine cavity. As the saline enters, the ultrasound captures images in real time. You may feel cramping as the uterus fills, similar to menstrual cramps. The clinician looks at the uterine walls from multiple angles, checking for polyps, fibroids, or other irregularities. Once enough images have been captured, the catheter is removed and the saline drains out naturally.
When It Should Be Scheduled
Timing matters for accuracy. The best window is during the first 10 days of your menstrual cycle, after bleeding has stopped but before ovulation. This is typically days 6 through 11. During this phase, the uterine lining is at its thinnest, which makes abnormalities much easier to spot. Research on timing found that scheduling the procedure in the second half of the cycle (days 16 through 28) produced a false-positive rate of 27%, meaning the thicker lining mimicked problems that weren’t actually there. Procedures done in the first 10 days had zero false positives.
If you’re postmenopausal, on continuous birth control pills, or have a hormonal IUD, the lining stays thin consistently, so the procedure can be scheduled at any time.
Pain, Risks, and Recovery
Most women describe the discomfort as mild to moderate cramping, concentrated around the moments when the catheter is inserted and when saline fills the uterus. The cramping is temporary and typically subsides quickly after the procedure. Taking an over-the-counter pain reliever like ibuprofen about 30 to 60 minutes beforehand can help.
Complications are uncommon. In a study of over 750 procedures, only 3.4% of patients experienced any side effects at all, and all were minor. The most common complaint was abdominal cramps (about half of those who had any issue), followed by light vaginal bleeding and vaginal discharge. Serious complications like infection are rare. The procedure is not performed during pregnancy or if you have an active pelvic infection, as introducing saline into the uterus in those situations could cause harm.
Recovery is straightforward. You can expect some light spotting or watery discharge for a day or two as the remaining saline drains. Most women return to normal activities the same day. There are generally no restrictions on exercise, bathing, or sexual activity afterward, though your doctor may give you specific instructions based on your situation.
What the Results Can Show
Your doctor typically reviews the images during or immediately after the procedure, so you may get preliminary results the same day. Normal results show a smooth, uniform uterine lining with no masses or irregularities. Abnormal findings might include polyps (small growths on the lining), submucosal fibroids (fibroids that bulge into the uterine cavity), adhesions (bands of scar tissue, sometimes from prior surgeries), a uterine septum (a wall of tissue dividing the cavity), or signs of endometrial hyperplasia or thickening.
If something abnormal is found, the next step depends on the specific finding. Small polyps may be monitored or removed with a hysteroscopy. Fibroids distorting the cavity might require surgical treatment if they’re causing symptoms or affecting fertility. Adhesions can sometimes be addressed with a minor procedure. The SIS itself is purely diagnostic: it identifies the problem but doesn’t treat it. What it does exceptionally well is give your doctor the information needed to decide whether further intervention is necessary or whether watchful waiting is the right approach.