An HSG test, short for hysterosalpingogram, is an X-ray imaging procedure that lets your provider see inside your uterus and fallopian tubes. It’s one of the most common tests ordered during a fertility workup because it can reveal two of the most frequent structural causes of infertility: blocked fallopian tubes and an irregularly shaped uterus. The whole procedure typically takes about 10 minutes.
How the Test Works
During an HSG, a thin catheter is placed through the cervix and into the uterus. A contrast dye (containing iodine) is then slowly injected through the catheter. As the dye fills the uterine cavity and flows into the fallopian tubes, a series of real-time X-ray images called fluoroscopy captures the shape and path of the dye. If your tubes are open, the dye spills freely out the ends into the surrounding pelvic area. If a tube is blocked, the dye stops at the point of obstruction, and that shows up clearly on the images.
The test is unique because no other single imaging method can evaluate both the inner shape of the uterus and whether the fallopian tubes are open in one sitting. Ultrasound can show the uterus well but doesn’t map the tubes the same way. That’s why HSG is often the first-line test for tubal assessment, sometimes combined with ultrasound or other imaging for a more complete picture.
Why Your Provider Ordered It
The primary reason for an HSG is to investigate infertility. If you’ve been trying to conceive without success, your provider needs to rule out physical barriers. Roughly 25 to 35 percent of female infertility involves a tubal factor, so confirming the tubes are open is a critical early step.
Beyond tubal blockages, the test can also detect structural abnormalities of the uterus. These include a uterus with an unusual shape (like a unicornuate uterus, which appears banana-shaped on imaging and has only one functioning tube), polyps or fibroids protruding into the uterine cavity, scar tissue or adhesions inside the uterus, and congenital variations in the fallopian tubes themselves. Any of these findings can affect your ability to conceive or carry a pregnancy.
What It Feels Like
Pain during an HSG varies widely from person to person, but the numbers give a useful picture. In one study comparing pain levels on a 0-to-10 scale, the median pain score during HSG was 5. About 39 percent of women rated it worse than menstrual cramps, while the rest found it comparable or milder. The discomfort comes mainly from the dye filling and stretching the uterine cavity and tubes.
The good news: for about 65 percent of women, the pain disappears immediately once the procedure ends. Taking an over-the-counter pain reliever like ibuprofen about 30 to 60 minutes beforehand can help take the edge off the cramping. The contrast injection itself typically lasts around 10 minutes, though it can range from 3 to 31 minutes depending on anatomy and findings.
When It’s Scheduled
An HSG is performed during a specific window of your menstrual cycle, typically between days 6 and 12 (after your period ends but before ovulation). This timing serves two purposes: it ensures you’re not pregnant, and the uterine lining is thin enough at this point in the cycle that the dye can clearly outline the cavity without being obscured by thicker tissue. Your provider will likely confirm you’re not pregnant before proceeding.
Understanding Your Results
Results fall into a few main categories. “Patent” tubes mean the dye flowed through both fallopian tubes and spilled into the pelvis normally. This is the result you want, and it rules out tubal blockage as a cause of infertility.
If dye stops partway through a tube, it can mean one of two things. A tubal obstruction may be temporary, caused by a muscle spasm during the procedure. A tubal occlusion is permanent structural damage, often from conditions like prior infections, endometriosis, or a fluid-filled tube called a hydrosalpinx. The blockage can be in one tube (unilateral) or both (bilateral), and it can occur at different points along the tube, from the section nearest the uterus to the far end near the ovary.
Your provider may also note uterine findings like polyps, fibroids pushing into the cavity, adhesions, or a congenital shape variation. Sometimes a follow-up test like hysteroscopy (a camera inserted into the uterus) is needed to confirm or further investigate what the HSG revealed.
The Unexpected Fertility Benefit
One of the more surprising aspects of HSG is that the procedure itself may improve your chances of getting pregnant, particularly when an oil-based contrast dye is used. A large randomized controlled trial in the Netherlands found that oil-based contrast increased the pregnancy rate by 10 percent compared to water-based contrast in the six months following the test. A separate study found clinical pregnancy rates of 51 percent in the oil-based group versus 27 percent in a non-oil-based group.
The exact reason isn’t fully understood, but the leading theory is that the dye may flush out minor debris or mucus plugs from the tubes, or that oil-based contrast may create a more favorable environment for implantation. The Australian Reproductive Endocrinology and Infertility Consensus Expert Group has formally recommended oil-based contrast for women with unexplained infertility undergoing HSG. If you have a choice, it’s worth asking your provider which type of contrast they use.
Risks and Side Effects
HSG is a low-risk procedure overall. The most serious potential complication is pelvic infection, which occurs in only about 0.3 to 0.4 percent of cases. Some providers prescribe a preventive antibiotic beforehand, though infection rates are similarly low with or without prophylaxis.
Allergic reactions to the iodine-based contrast are extremely rare, occurring in fewer than 0.1 percent of procedures. No anaphylactic reactions were reported in a large nationwide survey. Both oil-based and water-based contrast dyes contain iodine, which can temporarily affect thyroid function after the test. Oil-based contrast has a higher iodine concentration (480 mg/ml versus 240 to 300 mg/ml for water-based), so your provider may monitor thyroid levels if you have a preexisting thyroid condition.
After the procedure, you may notice light spotting or a small amount of watery discharge as the contrast dye drains out. Mild cramping for a few hours is normal. Most women return to their regular activities the same day.