An SIS ultrasound, short for saline infusion sonohysterography, is a diagnostic imaging procedure that uses sterile saltwater to expand the uterine cavity so doctors can see its interior in sharper detail than a standard ultrasound allows. The whole visit takes about 30 to 45 minutes, and the saline portion itself lasts only 5 to 10 minutes. It’s commonly ordered to investigate abnormal uterine bleeding, infertility, or recurrent pregnancy loss.
How It Works
During a regular transvaginal ultrasound, the walls of the uterus are pressed together, making it difficult to distinguish small growths or subtle abnormalities along the lining. An SIS changes this by filling the uterine cavity with a small amount of sterile saline through a thin catheter. The fluid separates the uterine walls, creating a clear contrast between the lining and any abnormal tissue. This lets the clinician evaluate each layer of the endometrium individually and outline lesions that would otherwise blend into the surrounding tissue.
The result is a real-time image that can distinguish between focal problems (like a polyp growing from one spot) and diffuse ones (like thickening spread across the entire lining). That distinction matters because it directly affects what treatment, if any, is recommended.
Why Doctors Order an SIS
The most common reason is abnormal uterine bleeding, whether you’re premenopausal or postmenopausal. An SIS can reveal the specific cause of that bleeding, such as polyps, fibroids that bulge into the uterine cavity (called submucosal fibroids), or adenomyosis, a condition where tissue similar to the uterine lining grows into the muscular wall of the uterus.
Infertility workups are another frequent indication. Adhesions (scar tissue inside the uterus) can interfere with implantation and are a known cause of reduced menstrual flow, recurrent miscarriage, and difficulty conceiving. An SIS can detect these adhesions clearly. Congenital uterine anomalies, meaning structural differences present from birth, are found in about 8% of women experiencing infertility and over 13% of those with recurrent miscarriages. An SIS can identify many of these structural variations.
The procedure can also check whether the fallopian tubes are open. When saline is pushed into the uterine cavity and fluid is later seen collecting near the ovaries, it confirms that at least one tube is unblocked. Since tubal factors play a role in 20 to 30% of infertile couples, this assessment is a routine part of fertility evaluations. A variation using saline mixed with tiny air bubbles can make tubal flow even easier to track on the ultrasound screen.
How Accurate It Is
For detecting endometrial polyps in women with abnormal bleeding, SIS has a sensitivity of 87% and a specificity of 86%. In comparison, a standard transvaginal ultrasound catches only about 62% of polyps, with a specificity of 73%. In practical terms, an SIS is significantly less likely to miss a polyp and less likely to flag something as abnormal when it isn’t. This improved accuracy often helps patients avoid more invasive procedures or, when surgery is needed, gives surgeons a clearer picture of what they’re dealing with before they go in.
What the Procedure Feels Like
You’ll undress from the waist down and lie on an exam table with your knees bent. The clinician first inserts a slim ultrasound wand (the same device used in a standard vaginal exam) to get an initial look at the uterus. A speculum is then placed to access the cervix, which may be wiped clean.
Next, a thin, flexible catheter is threaded through the cervical opening. This is the step most patients notice: it typically causes a pinching or cramping sensation similar to a menstrual cramp. Once the catheter is in place, the speculum is removed and the ultrasound wand is reinserted. Saline flows through the catheter to expand the uterine cavity while the wand captures real-time images. You may feel pressure or cramping as the uterus fills with fluid, but the active imaging portion lasts only 5 to 10 minutes.
How to Prepare
The procedure is typically scheduled during the first half of your menstrual cycle, after bleeding has stopped but before ovulation. At this point the uterine lining is at its thinnest, which makes abnormalities easier to spot and ensures you’re not pregnant.
If you’re not allergic, taking 800 milligrams of ibuprofen (four regular-strength Advil or Motrin tablets) about an hour beforehand can reduce cramping. You’ll be asked to empty your bladder right before the procedure starts, since a full bladder can obstruct the view of the uterus.
What to Expect Afterward
Mild cramping after the procedure is normal and generally resolves quickly. Some light spotting or watery discharge is common in the hours following, as the saline drains out. Most people return to their usual activities the same day without restrictions. Results are often available shortly after, sometimes discussed immediately while you’re still in the office, since the imaging happens in real time.