What Happens During an SIS Exam for a Uterine Polyp?

A saline infusion sonohysterogram (also called a sonohysterography or SIS) is an in-office imaging test used to get a clear view of the inside of the uterus. During the procedure, a doctor places a very small tube through the cervix, gently fills the uterine cavity with sterile saline (saltwater), and uses an ultrasound transducer to look for abnormalities like uterine polyps ^[1]. The saline safely distends the walls of the uterus, highlighting polyps that might otherwise be hidden on a standard ultrasound. While the procedure itself usually takes only a few minutes, knowing what to expect can help you feel more prepared and comfortable ^[2].

Scheduling and Preparation

For patients who menstruate regularly, an SIS is typically scheduled in the early follicular phase—the days right after your period ends but before you ovulate ^[3]. During this window, the lining of the uterus is thin, which makes it much easier to spot a polyp. If you have irregular cycles, do not menstruate, or are postmenopausal, your clinic will individualize the timing of your test.

The test cannot be performed if there is any chance you might be pregnant ^[4]. Your doctor’s office will likely require a pregnancy test, but because tests can miss very early pregnancies, they may also instruct you to avoid unprotected intercourse between your last period and the test.

You should ask your doctor about pain management before your appointment. Depending on your health history—such as allergies, stomach ulcers, kidney disease, or blood thinner use—your doctor may suggest taking an over-the-counter pain reliever like ibuprofen or acetaminophen beforehand. Research has shown that local anesthetics, such as lidocaine gel applied to the cervix, are not consistently beneficial for reducing discomfort during this procedure ^[5].

Step-by-Step: What Happens in the Room

The setup for an SIS is very similar to a routine pelvic exam. Here is the general sequence of events ^[1]:

1. Speculum Placement: You will lie back on an exam table with your feet in stirrups. The doctor will insert a speculum into your vagina to see your cervix.
2. Catheter Insertion: A thin, flexible tube called a catheter is gently guided through the cervical opening and into the lower part of the uterus.
3. Speculum Removal: Once the catheter is in place, the speculum is carefully removed.
4. Ultrasound Transducer: A transvaginal ultrasound transducer (a slender wand that uses sound waves, not a camera) is inserted into the vagina.
5. Saline Infusion and Imaging: The doctor will slowly push sterile saltwater through the catheter. As the fluid distends the uterine cavity, the doctor will watch the ultrasound screen in real time to take pictures of the cavity and any polyps.

In one large study, the actual procedure took an average of about 6 minutes ^[2]. However, the total visit will take longer to allow time for check-in, preparation, discussion of the procedure, and recovery.

Expected Sensations and Discomfort

Patient experiences with SIS vary. Many people feel pressure or cramping as the catheter is placed and as the fluid expands the uterus. In one study, premenopausal participants frequently described the sensation as crampy or gnawing ^[6]. However, severe pain is not the norm; the same study noted that 41% of participants across the study groups reported feeling no pain at all during the procedure ^[6].

Because the procedure involves touching the cervix, some patients may experience a vasovagal response—a sudden, temporary drop in heart rate and blood pressure that causes dizziness, sweating, or fainting. If you feel lightheaded or if the pain becomes too intense, tell your medical team immediately. You always have the right to ask the clinician to pause or stop the procedure.

Risks and When to Postpone

An SIS is a safe procedure. In a study of over 700 patients, minor complications occurred in about 3.4% of cases and were mostly temporary abdominal cramps, light vaginal bleeding, or watery discharge ^[2].

Serious complications are rare:

• Infection: Pelvic infections following an SIS are rare. Routine preventive antibiotics are generally not recommended for everyone ^[7]. However, if you have a history of pelvic inflammatory disease (PID) or dilated fallopian tubes (hydrosalpinx), your doctor may recommend antibiotics based on your individual risk ^[7][8]. Rarely, severe infections like a tubo-ovarian abscess (a pocket of pus involving the fallopian tube and ovary) have been reported ^[9].
• Ovarian Torsion: If you already have very large ovarian cysts, there is an extremely rare reported risk that the cyst could twist (a painful emergency called ovarian torsion) following the procedure ^[10].

The test should be postponed if you have an active pelvic infection, unexplained heavy bleeding, or if there is any chance of pregnancy ^[4].

Aftercare and Next Steps

After the test, the saline will leak out of your vagina. The clinic will provide you with a sanitary pad to manage the watery discharge and any light spotting, which may last for a day or two ^[2]. You should follow your clinic’s specific instructions regarding whether you can use tampons, take baths, or have intercourse afterward.

While light cramping is normal, you should seek emergency medical care if you develop:

• Sudden, severe, or worsening one-sided pelvic pain (especially with nausea or vomiting) ^[10]
• Fainting or severe dizziness

You should contact your doctor’s office for advice if you develop:

• A fever (ask your clinic for their specific temperature threshold, typically over 100.4°F or 38°C) ^[9]
• Foul-smelling vaginal discharge
• Heavy bleeding (such as soaking through a pad in an hour)

Because the doctor watches the ultrasound in real time, they may discuss preliminary findings with you immediately, though a formal final report will take more time. If an SIS finds a polyp, it provides an excellent view of its location and size, but it cannot test the tissue for cancer. The reference method for testing tissue and definitively ruling out malignancy is a hysteroscopy with biopsy—a procedure where a clinician looks inside the uterus and removes the polyp for laboratory testing ^[11]. However, not every polyp requires removal; your doctor will help you decide on the best next steps based on your symptoms, age, bleeding patterns, and fertility goals.