If you are consulting a specialist for difficulty conceiving, they will likely recommend evaluating your reproductive organs. The two primary scans for this are a Hysterosalpingogram (HSG) and a Saline Infusion Sonohysterography (SIS).
While both involve injecting fluid into the womb, they use different imaging technologies and check for different fertility issues.
Hysterosalpingogram (HSG): Checking the tubes
An HSG is a live X-ray scan (fluoroscopy). A liquid dye (contrast) is injected through your cervix into your womb, and X-ray images are taken as the dye flows through your fallopian tubes and spills into your pelvis.
- Primary focus: Checking if your fallopian tubes are open (patent) or blocked. Blocked fallopian tubes prevent the egg and sperm from meeting, which is a major cause of infertility.
- How it feels: You will feel moderate to intense cramping, similar to severe period pain, when the dye is injected. The cramping usually lasts for only a few minutes.
- Safety callout: Because it uses X-rays, it is scheduled strictly in the first half of your cycle (days 5 to 12) to ensure you are not pregnant.
Saline Infusion Sonohysterography (SIS): Checking the womb
An SIS (also called a saline scan or water scan) is an ultrasound test. Sterile saline (salty water) is injected through a catheter into your womb, and a transvaginal ultrasound probe is used to capture images.
- Primary focus: Examining the inside of the womb (uterine cavity). The saline stretches the womb walls, allowing the ultrasound to clearly show issues like polyps, fibroids, scar tissue, or congenital womb shapes.
- How it feels: You will feel mild to moderate cramping as the saline is introduced, which is generally milder than the cramping felt during an HSG.
- Safety callout: Like HSG, it is scheduled in the early part of your cycle to avoid disrupting a potential early pregnancy. It uses sound waves, so there is zero radiation.
Side-by-side comparison
| Feature | HSG | SIS | | :--- | :--- | :--- | | Technology | Live X-ray (Radiation) | Ultrasound (Sound waves) | | Main Target | Fallopian tubes | Uterine cavity (womb lining) | | Fluid Used | Contrast dye (iodine-based) | Sterile saline (salty water) | | Discomfort | Moderate to severe cramping | Mild to moderate cramping |
A practical close
If your doctor needs to check if your tubes are open, they will order an HSG. If they need to check if a fibroid or polyp is blocking the womb cavity, they will order an SIS. Discuss pain relief options (like taking ibuprofen one hour before) with your doctor to make the procedure as comfortable as possible.