What does SIS mean in medical terms?

If "SIS" has appeared in a letter, on a referral, or in something a doctor said, it almost certainly means a scan of your womb.

Medical letters are full of abbreviations nobody explains. Here is this one, in plain English.

Why you might be offered one

A normal ultrasound shows the womb from the outside in. The saline gently opens the cavity so the inside walls can be seen properly. It is often used to look into:

• heavy, irregular or prolonged periods
• bleeding between periods, after sex, or after the menopause
• a thickened lining seen on an earlier scan
• difficulty getting pregnant, or repeated miscarriage

It can show polyps, fibroids growing into the cavity, scar tissue (adhesions), or a womb that is shaped differently. Sometimes it shows that everything looks normal, which is useful to know too.

It is not the same as a HyCoSy, which uses a special fluid to check whether the fallopian tubes are open. Some clinics do both at one appointment. If you're not sure which you're having, ask.

Before the scan

• Timing: it is usually booked just after your period has finished and before you ovulate, when the lining is thinnest. If your appointment lands during your period, ring the clinic and ask whether to rearrange.
• Pregnancy: it shouldn't be done if you could be pregnant. You may be asked to avoid unprotected sex from the start of your period until the scan, or to take a pregnancy test on the day.
• Infection: tell them if you have unusual discharge, a temperature or pelvic pain, as an infection would need treating first.
• Pain relief: many clinics suggest taking a painkiller you normally use for period pain about an hour beforehand. Check your appointment letter, and only take what's safe for you.
• Bring a pad for afterwards.

What happens

1. You'll lie on a couch, undressed from the waist down, with a sheet over you. You can ask for a chaperone.
2. An internal (transvaginal) ultrasound probe is used first to look at the womb and ovaries.
3. The probe is removed and a speculum is inserted, like a smear test. The cervix is cleaned.
4. A very thin, soft tube is passed through the cervix into the womb, and the speculum is taken out.
5. The probe goes back in and saline is slowly run through the tube while the images are taken. This part usually takes a few minutes.
6. The tube and probe are removed and you can get dressed.

The whole appointment is usually around half an hour. You can ask them to pause or stop at any point.

Does it hurt?

Most people feel cramping or pressure, a lot like period pain, mainly while the saline goes in. For some it's mild, for others it's properly uncomfortable. Both are normal, and it's fine to say so at the time.

Afterwards you may have some watery discharge as the saline comes out, light spotting, and mild cramps for a few hours. A pad, a hot water bottle and your usual painkiller usually help.

Call your GP or the clinic, or NHS 111, if in the next few days you have a temperature, pain that's getting worse rather than better, heavy bleeding, or smelly discharge. Infection is rare, but these are the signs.

Questions worth asking

1. What are you hoping this scan will show, or rule out?
2. Is this an SIS only, or are my tubes being checked too?
3. Will I be told anything today, or will the results go to my GP or consultant?
4. If something is found, what usually happens next?
5. Who do I contact if I haven't heard anything, and by when?

Write the answers down before you leave. It's surprisingly easy to forget what was said once you're back in the car.

Keeping track of it in SIS

And no, this isn't the same SIS. Ours stands for Seen. Informed. Supported. (and, warmly, Sisters in Solidarity). It's a free, private app for keeping your health story in one place. If you're having this scan, this is how it fits in:

• Before: add the appointment under What's coming on the home screen, so it sits alongside the symptoms that led to it.
• On the day: add the scan in Tests & scans, and note who you saw, what you were told and what happens next in the appointment.
• The letter: photograph it into Documents & letters, so it's there next time someone asks "have you had that done?"
• Afterwards: if the cramps or bleeding go on longer than you expected, note it. That's exactly the kind of detail that gets lost between appointments.

When you go back to talk about the results, the Doctor summary puts the scan, your symptoms and your history on one page. So the story walks in with you.

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Important: this page is general information, not medical advice. Clinics do things slightly differently, so follow the instructions in your own appointment letter. If you have severe pain, very heavy bleeding, fainting, or you feel very unwell, seek urgent medical help (NHS 111, or 999 in an emergency).

Sources:
Cleveland Clinic, Sonohysterogram.
American Society for Reproductive Medicine, Saline infusion sonohysterogram (SHG).
Women and Newborn Health Service, Saline infusion sonography and hystero contrast salpingography (patient leaflet).
Last reviewed: October 2026.