A saline infusion sonogram goes by several names: SIS, saline sonohysterogram, or simply "the water ultrasound." Whatever your clinic calls it, the procedure fills your uterine cavity with sterile saline during a transvaginal ultrasound, and the resulting images can reveal problems that a standard ultrasound misses entirely.
What a Saline Sonogram Detects
The saline acts as a contrast medium. By distending the uterine cavity, it separates the endometrial walls and creates a clear outline of structures that would otherwise appear as a single, compressed layer on a regular transvaginal scan.
SIS is particularly good at identifying:
- Endometrial polyps: Small growths on the uterine lining that can interfere with implantation. Polyps are common (prevalence of 10 to 24 percent in subfertile women) and frequently missed on standard ultrasound.
- Submucosal fibroids: Fibroids that protrude into the uterine cavity. Their location, not just their size, determines whether they affect fertility.
- Uterine septum: A band of tissue dividing the cavity, associated with recurrent pregnancy loss. SIS can suggest the presence of a septum, though MRI is the gold standard for confirming the type of uterine anomaly.
- Intrauterine adhesions (Asherman syndrome): Scar tissue from prior procedures (D&C, C-section) that can reduce the functional surface area of the endometrium.
SIS vs. HSG: How They Differ
Both tests evaluate the uterine cavity, but they are not interchangeable. The differences matter for deciding which test your situation actually needs.
| Feature | SIS (Saline Sonogram) | HSG (Hysterosalpingogram) |
|---|---|---|
| Imaging method | Ultrasound (no radiation) | X-ray fluoroscopy |
| Contrast medium | Sterile saline | Iodine-based dye |
| Shows tubal patency | No (limited assessment) | Yes (primary purpose) |
| Shows cavity detail | Excellent | Good for large defects, limited for small polyps |
| Pain level (typical) | Mild cramping | Moderate cramping to sharp pain |
| Cost (US, uninsured) | $200 to $600 | $500 to $1,500 |
| Timing in cycle | Day 5 to 12 (follicular phase) | Day 5 to 12 (follicular phase) |
| Iodine allergy concern | None | Yes (shellfish/iodine allergy screening) |
Which Test Do You Need?
If the question is "are my tubes open," you need an HSG. If the question is "is there something inside my uterus that could interfere with implantation," SIS gives a better answer. Many fertility workups include both. Some clinics use HyCoSy (a saline-and-contrast hybrid that evaluates both cavity and tubes on ultrasound) as a single combined test.
How to Prepare
The preparation is straightforward, but a few details reduce discomfort:
- Schedule during the follicular phase (after your period ends but before ovulation, typically cycle day 5 to 12). The endometrium is thinnest, making structures easier to see, and there is no risk of disrupting an early pregnancy.
- Take ibuprofen 30 to 60 minutes before. Most clinics recommend 400 to 600 mg. This reduces uterine cramping during and after the procedure.
- Eat normally. No fasting required.
- Expect the appointment to last 15 to 30 minutes total, though the saline infusion itself takes only 3 to 5 minutes.
- Bring a pad. Saline and a small amount of blood will leak out afterward. This is normal and resolves within hours.
What the Procedure Feels Like
Descriptions range from "barely noticed it" to "intense cramping for about 60 seconds." The variation is real and depends on factors like cervical anatomy, the provider's technique, and individual pain sensitivity.
The sequence: speculum insertion (similar to a Pap smear), a thin catheter passed through the cervix, speculum removal, transvaginal ultrasound probe insertion, then slow saline infusion. The cramping, when it occurs, happens during the saline push. Most patients describe it as period-like cramps that peak for 30 to 90 seconds and then fade.
If you have a history of cervical stenosis (a tight or scarred cervix), let your provider know in advance. They may use a smaller catheter or apply topical anesthetic to the cervix.
Reading the Results
Results are usually available immediately because your provider is reading the ultrasound images in real time. Common findings and what they mean:
- Normal cavity: Smooth, symmetrical walls with no filling defects. No action needed.
- Polyp identified: Polypectomy (removal via hysteroscopy) is typically recommended before IVF or IUI. Polyps larger than 1 to 1.5 cm are associated with reduced implantation rates.
- Submucosal fibroid: Location and size determine whether surgical removal (myomectomy) is warranted. Fibroids distorting the cavity are more likely to affect outcomes than intramural fibroids of the same size.
- Possible septum: Additional imaging (3D ultrasound or MRI) is usually ordered to distinguish a septum (surgically correctable) from a bicornuate uterus (usually not corrected).
- Adhesions: Hysteroscopic lysis (cutting the scar tissue under direct visualization) is the standard treatment.
A Normal SIS Does Not Mean Everything Is Normal
SIS evaluates the uterine cavity only. It does not assess tubal patency, ovarian reserve, sperm parameters, or hormonal function. A complete fertility workup includes SIS or HSG alongside blood work (AMH, FSH, estradiol, TSH) and semen analysis.
Cost and Access Considerations
SIS is widely available at reproductive endocrinology practices and many OB-GYN offices with ultrasound capability. Not all OB-GYNs perform the procedure in-house; you may be referred to a specialist or imaging center. Wait times vary from same-week scheduling at large fertility clinics to 2 to 4 weeks at general OB-GYN practices.
Uninsured cost in the United States typically ranges from $200 to $600 for the procedure itself, plus any associated office visit fees. This is substantially less than an HSG ($500 to $1,500) and considerably less than hysteroscopy ($1,500 to $5,000), which provides direct visualization of the cavity but requires anesthesia and an operating room.
When billed as part of an infertility evaluation, SIS is more likely to be covered by insurance than when ordered as a standalone imaging study. The diagnostic code (CPT 76831 for saline infusion sonohysterography) is specific to this procedure. If your insurer requires pre-authorization, have your provider submit it with the infertility diagnosis code (N97.x series) rather than a general pelvic pain code.
SIS vs. 3D Ultrasound vs. Hysteroscopy
SIS is not the only tool for evaluating the uterine cavity, and understanding when each is appropriate prevents unnecessary repeat procedures:
- Standard 2D transvaginal ultrasound: Adequate for ovarian assessment and follicle monitoring. Limited for intracavitary pathology because the walls are apposed (touching). Misses roughly 40 to 50 percent of polyps and submucosal fibroids that SIS would detect.
- 3D ultrasound: Better than 2D for evaluating uterine shape (septum vs. bicornuate). Can be combined with saline infusion (3D SIS) for the most detailed non-surgical cavity assessment. Not universally available.
- Hysteroscopy: Direct camera visualization of the cavity. The gold standard, but it requires anesthesia, is more expensive, and is typically reserved for when treatment (polyp removal, septum resection, adhesion lysis) is planned, not just diagnosis.
- MRI: Best for classifying Mullerian anomalies (uterine malformations) when SIS or 3D ultrasound raises suspicion. Expensive ($1,000 to $3,000) and not a first-line screening tool.
When SIS Is Part of the Fertility Workup Sequence
In a standard fertility evaluation, SIS or HSG is typically performed after initial blood work (AMH, FSH, estradiol, TSH, prolactin) and semen analysis, and before proceeding to treatment. The rationale: there is no point optimizing ovulation and sperm delivery if a structural cavity problem would prevent implantation regardless.
Some clinics perform SIS as the default cavity assessment for all fertility patients. Others reserve it for patients with specific risk factors (prior uterine surgery, recurrent miscarriage, abnormal uterine bleeding) and use HSG as the primary initial test because it evaluates both tubal patency and cavity in one procedure. Both approaches are reasonable; ask your provider which they recommend for your situation and why.
If SIS identifies a polyp, fibroid, or adhesion, the next step is typically hysteroscopy for treatment. This should happen before starting IUI or IVF cycles. The recovery from hysteroscopic polypectomy or adhesion lysis is minimal (1 to 2 days of cramping, then normal activity), and most patients can begin treatment the following cycle.
Emotional Preparation for the Results
Most SIS results are normal, and the relief of a normal result is significant. If an abnormality is found, it is almost always treatable. Polyps are removed in a quick outpatient procedure. Fibroids can be addressed surgically or monitored depending on size and location. Adhesions are lysed hysteroscopically. Even a uterine septum, which sounds alarming, has a straightforward surgical solution (hysteroscopic metroplasty) when indicated.
The worst outcome of an SIS is not finding a problem. It is skipping the test and discovering the problem after failed treatment cycles. A 15-minute diagnostic procedure that might save months of unsuccessful treatment is consistently underutilized in fertility care.
Recovery and What Comes After
Post-procedure recovery is minimal. Most patients describe mild cramping that resolves within an hour and light spotting or watery discharge for the remainder of the day as the saline drains. You can resume all normal activities immediately, including work, exercise, and intercourse. No prescription medications are needed afterward, though you can continue ibuprofen as needed for any residual cramping.
If your SIS reveals a finding that requires treatment (polyp, submucosal fibroid, or adhesions), your provider will typically schedule a hysteroscopic procedure before your next treatment cycle. The gap between SIS and hysteroscopy can be as short as one to two weeks at large fertility practices, or two to four weeks at general OB-GYN offices. If your SIS is normal, you move directly into treatment planning with the confidence that the uterine cavity is clear and ready for implantation. This peace of mind is one of the underappreciated benefits of the test, even when the result is simply "normal."