Saline Infusion Sonogram (SIS) — What to Expect & Why It's Done

Before an embryo transfer, before a complicated IUI cycle, or simply as part of an unexplained infertility workup — your doctor may order a saline infusion sonogram (SIS), also called a saline hysterosonogram (SHG) or sonohysterography. Despite its unfamiliar name, it is one of the most straightforward and informative tests in reproductive medicine.

This guide explains what a SIS is, how it compares to other uterine evaluation tools, exactly what happens during the procedure, what it can and cannot detect, and how results guide your fertility treatment plan.

What Is a Saline Infusion Sonogram?

A saline infusion sonogram is an in-office ultrasound procedure in which a small amount of sterile saline (salt water) is gently injected into the uterine cavity through a thin catheter placed through the cervix. As the saline fills and expands the uterine cavity, a transvaginal ultrasound probe captures real-time images.

The logic is simple: a collapsed uterine cavity is difficult to evaluate clearly on standard ultrasound because the front and back walls touch each other. Saline acts as a contrast medium — separating the walls and revealing the interior surface of the cavity in detail.

Think of it as the difference between trying to see the inside of a deflated balloon (standard ultrasound) versus an inflated one (SIS).

SIS vs. HSG vs. Standard Ultrasound: Key Differences

All three tools evaluate the female reproductive tract, but they serve different purposes and have different strengths.

The SIS and HSG are complementary, not interchangeable. HSG evaluates whether the tubes are open; SIS evaluates the uterine cavity in detail. Most IVF programs require both before proceeding to embryo transfer.

What Does SIS Detect?

SIS is specifically designed to find intrauterine abnormalities — problems inside the uterine cavity that can impair implantation, cause pregnancy loss, or complicate fertility treatment.

1. Endometrial Polyps

Polyps are overgrowths of the endometrial lining — finger-like projections that protrude into the uterine cavity. They are extremely common (found in 10–25% of women undergoing fertility evaluation) and are a well-established cause of implantation failure.

On SIS, polyps appear as echogenic (bright) focal lesions projecting into the saline-filled cavity, often with a visible feeding blood vessel on color Doppler. Standard ultrasound frequently misses small polyps — SIS sensitivity for polyp detection is approximately 90%, compared to 50–60% for standard transvaginal ultrasound.

Removal of polyps (hysteroscopic polypectomy) is recommended before IVF and is associated with significantly improved pregnancy rates.

2. Submucosal Fibroids

Fibroids (leiomyomata) are benign smooth muscle tumors of the uterus. Their impact on fertility depends critically on their location relative to the uterine cavity:

SIS is particularly valuable for classifying submucosal fibroids, especially distinguishing:

• FIGO Type 0: Entirely within the cavity (pedunculated) — removable by hysteroscopy
• FIGO Type 1: <50% within the wall — removable by hysteroscopy
• FIGO Type 2: >50% within the wall — may require laparoscopy or alternative approach

3. Uterine Septum and Congenital Anomalies

A uterine septum — a fibrous band of tissue that partially or completely divides the uterine cavity — is the most common congenital uterine anomaly (prevalence ~1–3% in the general population; higher in women with recurrent miscarriage). Septum does not prevent pregnancy but is associated with significantly elevated first and second trimester miscarriage rates.

SIS, particularly 3D SIS, is excellent for differentiating:

• Arcuate uterus (minor indentation; clinically insignificant in most cases)
• Subseptate uterus (partial division; associated with miscarriage; treatable)
• Septate uterus (complete division; associated with miscarriage and preterm birth; treatable)
• Bicornuate uterus (two partially separate uterine horns; requires 3D imaging or MRI to confirm)

Surgical correction of a uterine septum (hysteroscopic metroplasty) is associated with reduced miscarriage rates and improved live birth rates.

4. Intrauterine Adhesions (Asherman's Syndrome)

Intrauterine adhesions (synechiae) are scar tissue bands within the uterine cavity, typically resulting from prior uterine surgery (dilation and curettage, especially for pregnancy-related procedures), infection, or prior hysteroscopy. They range from thin filmy bands to dense, obliterative scarring.

Adhesions can reduce uterine cavity volume, distort the cavity, and impair endometrial function — reducing implantation rates and increasing miscarriage risk.

On SIS, adhesions appear as irregular, fixed bands crossing the cavity or as areas where saline cannot adequately fill. Definitive diagnosis requires hysteroscopy — but SIS serves as an excellent screening tool.

5. Endometrial Thickening or Abnormalities

SIS allows detailed assessment of endometrial thickness and echogenicity at specific cycle phases. It can identify areas of focal thickening, heterogeneous texture, or irregular borders that may suggest endometritis (uterine cavity infection), endometrial hyperplasia, or early malignancy — all conditions requiring further evaluation before fertility treatment.

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The SIS Procedure: Step by Step

Before the Procedure

• Cycle timing: SIS should be scheduled between cycle days 5 and 11 — after your period ends but before ovulation. This timing ensures the endometrium is thin enough for clear imaging and eliminates the risk of disturbing a very early pregnancy.
• Antibiotic premedication: Some clinics prescribe a short course of doxycycline before the procedure to reduce infection risk, particularly if you have a history of pelvic infection.
• Pain management: Take ibuprofen 600–800 mg 30–60 minutes before the procedure. Most women find SIS only mildly uncomfortable with pre-medication.
• No fasting required: Unlike procedures requiring sedation, SIS needs no fasting or special preparation.

During the Procedure (15–20 Minutes Total)

1. Positioning: You lie on the exam table in the same position as a pelvic exam or Pap smear
2. Speculum insertion: A speculum is placed to visualize the cervix — same as a Pap smear
3. Catheter placement: A very thin catheter (SIS catheter, typically 5–7 Fr) is passed through the cervical opening into the uterine cavity. This step causes a brief cramping sensation for most women.
4. Speculum removal: The speculum is removed and the transvaginal ultrasound probe is inserted
5. Saline infusion: Sterile saline (typically 10–20 mL) is gently injected through the catheter while the sonographer captures ultrasound images of the expanding cavity in real time
6. Imaging: The sonographer systematically images the entire cavity, noting any abnormalities. 3D imaging may be captured if a structural anomaly is suspected.
7. Completion: The catheter is removed; saline drains naturally. You may have mild watery discharge for a few hours.

What You Will Feel

Most women describe SIS as:

• Mild to moderate cramping during catheter insertion and saline infusion — similar to menstrual cramps
• Brief pressure when the saline is injected
• Mild cramping that typically resolves within 30–60 minutes of the procedure

Women with cervical stenosis (a narrow cervical opening, often after prior cone biopsy, LEEP, or in nulliparous older women) may experience more difficult catheter placement and greater discomfort. Discuss this with your doctor beforehand — cervical dilation may be needed.

After the Procedure

• You can drive yourself home and return to normal activities immediately
• Mild cramping may persist for 1–4 hours; ibuprofen is usually sufficient
• Light spotting or watery discharge for 1–2 days is normal
• Avoid intercourse, tampons, and swimming for 24–48 hours (reduces infection risk)
• Contact your doctor if you develop fever, heavy bleeding, or severe pelvic pain — rare signs of infection

Cost and Insurance Coverage

Insurance coverage for SIS is generally good when performed as part of an infertility evaluation — it is coded as a diagnostic gynecological procedure. Pre-authorization requirements vary by plan. Ask your clinic's billing department to verify coverage before scheduling.

When Is SIS Ordered?

SIS is routinely ordered in the following clinical situations:

• Before IVF: Most fertility clinics require a normal SIS within 12 months before embryo transfer. An abnormal cavity — even a small polyp — can significantly reduce success rates.
• Before medicated IUI cycles: Some clinics include SIS as part of the pre-IUI evaluation.
• Recurrent pregnancy loss: Women with 2+ miscarriages need uterine cavity evaluation; SIS is a first-line tool. Endometriosis can also cause recurrent loss and impair implantation — the endometriosis and fertility hub explains how this condition is evaluated and treated.
• Recurrent implantation failure: After 2+ failed embryo transfers with good-quality embryos, SIS is repeated to ensure no new cavity pathology has developed.
• Abnormal uterine bleeding: Heavy, irregular, or intermenstrual bleeding warrants cavity evaluation.
• Abnormal standard ultrasound: When transvaginal ultrasound suggests endometrial thickening, irregular contour, or possible polyp.

What Happens Based on Results

In virtually all cases where SIS identifies a correctable abnormality, treatment is performed hysteroscopically — a minimally invasive procedure through the cervix requiring no incisions, usually done under brief sedation or anesthesia in an outpatient setting.

Limitations of SIS

Despite its excellent sensitivity for intrauterine pathology, SIS has limitations:

• Cannot assess tubal patency — HSG is still needed for that evaluation. For a full picture of every test in a female fertility workup, see the complete guide to fertility testing for women.
• Cannot visualize outside the uterus — endometriosis, ovarian cysts, and pelvic adhesions require laparoscopy or ultrasound
• Difficult in severely stenotic cervix — catheter placement may fail; hysteroscopy under anesthesia may be needed instead
• Timing-sensitive — must be done in the early follicular phase; scheduling errors reduce image quality
• Operator-dependent — image quality and interpretation depend on the sonographer's skill

SIS vs. Office Hysteroscopy: When to Go Straight to Camera

Some fertility clinics perform office hysteroscopy instead of SIS — placing a small camera directly into the uterine cavity (no saline required) to evaluate it in real time. This has the advantage of being both diagnostic and potentially therapeutic (small polyps can be removed at the same visit).

The choice between SIS and office hysteroscopy depends on:

• Availability of equipment and trained personnel
• Patient preference and pain tolerance
• Clinical suspicion (if polyp is already strongly suspected, going directly to hysteroscopy is efficient)
• Cost (office hysteroscopy may be more expensive)

Both approaches are acceptable first-line tools for uterine cavity evaluation before fertility treatment. Your clinic will recommend the approach that best fits their setup and your specific situation.

Key Takeaways

• SIS is a simple in-office procedure using transvaginal ultrasound and saline infusion to evaluate the uterine cavity interior — no radiation, no sedation
• It is superior to standard ultrasound for detecting polyps, submucosal fibroids, septum, and adhesions
• Ideal timing: cycle days 5–11; take ibuprofen beforehand; most women experience only mild cramping
• SIS does not assess tubal patency — HSG is still needed for that component
• Required by most IVF programs before embryo transfer; also indicated for recurrent loss and recurrent implantation failure
• Abnormal findings almost always have a hysteroscopic correction available before proceeding with fertility treatment

References

1. American Society for Reproductive Medicine (ASRM). Uterine septum: a guideline. Fertil Steril. 2016;106(3):530–540.
2. American Institute of Ultrasound in Medicine (AIUM). AIUM practice guideline for the performance of sonohysterography. J Ultrasound Med. 2015;34(8):1515–1522.
3. Seshadri S, El-Toukhy T, Douiri A, Jayaprakasan K, Khalaf Y. Diagnostic accuracy of saline infusion sonography in the evaluation of uterine cavity abnormalities prior to assisted reproductive techniques: a systematic review and meta-analyses. Hum Reprod Update. 2015;21(2):262–274.
4. Practice Committee of the ASRM. Endometrial polyps and infertility: a committee opinion. Fertil Steril. 2020;113(2):261–262.
5. Bosteels J, Kasius J, Weyers S, Broekmans FJ, Mol BW, D'Hooghe TM. Hysteroscopy for treating subfertility associated with suspected major uterine cavity abnormalities. Cochrane Database Syst Rev. 2015;(2):CD009461.

Frequently Asked Questions

Q: What is a saline infusion sonogram and how does it differ from a standard ultrasound? A: A saline infusion sonogram (SIS) uses a thin catheter to gently fill the uterine cavity with sterile saline while a transvaginal ultrasound captures real-time images. This separates the uterine walls — like inflating a balloon — revealing the interior surface in detail. Standard ultrasound, where the walls touch, has limited sensitivity for small polyps and submucosal fibroids. SIS sensitivity for polyp detection is approximately 90% compared to 50–60% for standard transvaginal ultrasound.

Q: Can a saline infusion sonogram also check if my fallopian tubes are open? A: No. SIS evaluates the uterine cavity interior but cannot assess tubal patency. An HSG (hysterosalpingography) is the standard test for confirming fallopian tubes are open and is required separately. Most IVF programs require both tests — SIS for the uterine cavity and HSG for tubal patency — before proceeding to embryo transfer.

Q: When in the menstrual cycle should a SIS be scheduled? A: SIS should be scheduled between cycle days 5 and 11 — after your period ends but before ovulation. This timing ensures the endometrium is thin enough for clear imaging and eliminates the risk of disturbing a very early pregnancy. Take ibuprofen 600–800 mg 30–60 minutes before the procedure; most women experience only mild cramping.

Q: What happens if a polyp or fibroid is found on the SIS? A: Endometrial polyps are removed by hysteroscopic polypectomy before IVF — removal is associated with significantly improved pregnancy rates. Submucosal fibroids (FIGO types 0–1) are also removed by hysteroscopy. Type 2 fibroids (more than 50% within the wall) may require a more involved approach. In virtually all cases where SIS identifies a correctable abnormality, hysteroscopic treatment is available before fertility treatment proceeds.

Q: How much does a saline infusion sonogram cost and is it covered by insurance? A: Self-pay costs range from $200–$450 at a fertility clinic, $300–$600 at a hospital outpatient setting, and an additional $50–$150 for 3D imaging if needed. Insurance coverage for SIS performed as part of an infertility evaluation is generally good — it is coded as a diagnostic gynecological procedure. Pre-authorization requirements vary by plan; confirm with your clinic's billing department before scheduling.

This article is for informational purposes only and does not constitute medical advice. Consult a board-certified reproductive endocrinologist for guidance on uterine cavity evaluation appropriate for your situation.