Hysterography, more commonly called hysterosalpingography or HSG, is an X-ray-based imaging procedure that maps the inside of the uterus and fallopian tubes by filling them with a contrast dye visible on fluoroscopy. It remains one of the standard first-line tests for evaluating tubal patency during a fertility workup, and it doubles as a tool for spotting structural abnormalities inside the uterine cavity. What makes the procedure unusual among diagnostic tests is that it also appears to have a therapeutic effect: pregnancy rates rise in the months after an HSG, particularly when an oil-based contrast medium is used.
What Happens During the Procedure
An HSG is typically performed in the first half of the menstrual cycle, after bleeding has stopped but before ovulation. This timing avoids disrupting an early pregnancy and also ensures the uterine lining is thin enough for a clear image. You lie on a fluoroscopy table, a speculum is placed, and the cervix is cleaned. A thin catheter is then inserted through the cervix, and contrast dye is slowly injected while X-ray images are captured in real time.
The dye fills the uterine cavity first, outlining its shape and revealing any irregularities such as polyps, fibroids, or structural malformations. As more dye is pushed through, it travels into the fallopian tubes. If a tube is open, the dye spills freely out the far end into the pelvic cavity. If the dye stops partway through or does not enter a tube at all, that suggests a blockage. The whole procedure usually takes under ten minutes.
Two main types of catheter are used: a traditional metal cannula (sometimes called an acorn cannula) and a flexible balloon catheter. A randomized trial comparing the two found that the balloon catheter required less contrast medium, less fluoroscopy time, and caused significantly less pain, with women in the balloon group reporting an average pain score of about 3.8 out of 10 compared with 5.6 in the metal-cannula group.1Human Reproduction. Hysterosalpingography with a balloon catheter versus a metal cannula: a prospective, randomized, blinded comparative study Subsequent studies have confirmed this pattern and also found the balloon catheter produces fewer side effects like nausea.2PubMed. Evaluation of pain during hysterosalpingography with the use of balloon catheter vs metal cannula A systematic evidence review concluded that high-quality evidence supports the balloon catheter for reducing procedural pain.3Rev. Assoc. Med. Bras.. Hysterosalpingography: Balloon Catheter or Metal Cannula?
Oil Versus Water Contrast and the Fertility Boost
The choice of contrast dye is one of the most actively studied questions in HSG. Two broad categories exist: oil-based contrast (typically ethiodized poppyseed oil, sold under brand names like Lipiodol) and water-soluble contrast. Both produce adequate diagnostic images, but their effects on subsequent fertility diverge in a way that has reshaped clinical practice.
A large Dutch randomized trial involving over 1,100 infertile women found that roughly 40% of women who received oil-based contrast achieved an ongoing pregnancy within six months, compared with about 29% in the water-based group. Live birth rates followed the same pattern, at around 39% versus 28%.4PubMed. Oil-Based or Water-Based Contrast for Hysterosalpingography in Infertile Women A separate multicenter trial in China confirmed the finding, reporting that oil-based contrast produced superior image quality and better fertility outcomes.5The Lancet. Efficacy and safety of ethiodized poppyseed oil for hysterosalpingography in infertile women: a multicentric, randomized, controlled clinical trial A meta-analysis pooling data from multiple trials estimated that oil-based contrast raised the odds of pregnancy by about 50% and the odds of live birth by roughly 60% compared with water-based dye.6PubMed Central. A meta-analysis of fertility and adverse outcomes in oil- and water-based contrast for hysterosalpingography
The exact mechanism behind this fertility-enhancing effect is not settled. Theories include flushing of debris from the tubes, disruption of thin adhesions, and an immunomodulatory effect of the oil on the endometrium. Whatever the reason, the observation has been reproduced consistently enough that some clinics now view HSG with oil-based contrast as a low-cost fertility intervention in its own right, not merely a diagnostic step. A retrospective cohort study in women with endometriosis found clinical pregnancy rates of about 51% in the oil group versus 27% in the water group, with live birth rates of roughly 31% versus 20%.7PubMed Central. Impact of oil-based contrast agents in hysterosalpingography on fertility outcomes in endometriosis: a retrospective cohort study
What HSG Can and Cannot Diagnose
HSG is considered a reference standard for assessing whether the fallopian tubes are open or blocked, and it is the only first-line imaging modality that shows the interior contour of both the tubal lumen and the uterine cavity in a single study.8PubMed. Evaluating Fallopian Tube Patency: What the Radiologist Needs to Know It also picks up conditions like hydrosalpinx (fluid-filled, dilated tubes) and salpingitis isthmica nodosa, a nodular thickening of the tube wall associated with infertility.
Inside the uterus, HSG can detect large polyps, submucous fibroids that distort the cavity, and intrauterine adhesions (Asherman syndrome). Its sensitivity for adhesions is reasonable, around 75% in comparative studies.9PubMed. Diagnostic accuracy of sonohysterography, transvaginal sonography, and hysterosalpingography in patients with uterine cavity diseases However, its ability to identify smaller polypoid lesions is considerably weaker, with sensitivity as low as 50% and a positive predictive value under 30% for polyps in the same study.
One well-known diagnostic blind spot involves congenital uterine malformations. HSG shows the internal shape of the cavity but cannot image the outer contour of the uterus. This means it can identify that the cavity has an unusual shape, but it often cannot tell you whether that shape results from a septum (a wall of tissue dividing the cavity, which can be surgically removed) or a bicornuate uterus (a deeper structural anomaly where the uterus itself has two horns). A retrospective study concluded that differentiating between these two conditions on HSG alone is unreliable and recommended additional imaging such as three-dimensional ultrasound.10PubMed. Is hysterosalpingography able to diagnose all uterine malformations correctly? A retrospective study Research comparing HSG to sonohysterography found that sonohysterography achieved 100% accuracy in distinguishing septate from bicornuate uterus, while HSG’s accuracy hovered around 80%.11PubMed. Diagnostic accuracy of sonohysterography, hysterosalpingography and diagnostic hysteroscopy in diagnosis of arcuate, septate and bicornuate uterus
Accuracy for Tubal Blockages
Tubal patency is the main event when it comes to HSG, but the test is not infallible. Laparoscopy with dye testing is considered the gold standard for confirming tubal disease, and studies comparing HSG against laparoscopy reveal a mixed picture. One study found HSG sensitivity for detecting tubal occlusion at 75%, with specificity of about 51% and overall accuracy of 58%.12Fertility & Reproduction. Comparison of Hysterosalpingography and Laparoscopy as Diagnostic Tool for Tubal Infertility in Bangladesh Another reported high sensitivity at nearly 92% but very poor specificity at 23%, meaning many women were flagged as having tubal problems when in fact they did not.13Ibrahim Cardiac Medical Journal. Diagnostic Accuracy of Hysterosalpingography as Compared to Laparoscopy in Detecting Tubal Factors of Infertility
A common culprit for false positives is tubal spasm. When the dye is injected, the muscular wall of the fallopian tube can clamp down reflexively, making an open tube look blocked. This is one reason fluoroscopy with real-time imaging is preferred: the operator can watch for spasm, pause, and re-inject to see whether the dye eventually flows through. A false negative can also occur when peritubal adhesions or endometriosis distort the outside of the tube without actually blocking the lumen. Laparoscopy identified peritubal adhesions and tubo-ovarian distortions in over 40% of cases that HSG missed entirely.14Ibrahim Cardiac Medical Journal. Diagnostic Accuracy of Hysterosalpingography as Compared to Laparoscopy in Detecting Tubal Factors of Infertility In practice, if HSG shows bilateral tubal blockage or suspicious findings, most clinicians follow up with laparoscopy before concluding the tubes are irreversibly damaged.
Managing Pain During the Test
Discomfort during HSG is one of the most common concerns for patients, and the research on pain management is surprisingly uneven. Pain levels vary widely from one person to the next and seem closely tied to factors like anxiety, the catheter type used, and whether the tubes are blocked (blocked tubes lead to more distension and more cramping).
A randomized trial comparing four pain-relief strategies found that taking a nonsteroidal anti-inflammatory drug alone resulted in average pain scores around 7 out of 10, while adding either topical lidocaine cream to the cervix or a paracervical lidocaine injection dropped scores to about 4-5 out of 10.15PubMed Central. Comparison of four different pain relief methods during hysterosalpingography: a randomized controlled study Interestingly, a different trial found that squirting lidocaine directly into the uterine cavity before the dye did not help at all and may have actually increased post-procedure pain.16PubMed. Transcervical intrauterine topical local anesthetic at hysterosalpingography: a prospective, randomized, double-blind, placebo-controlled trial The takeaway is that how and where the local anesthetic is applied matters more than whether one is given at all.
Anxiety is an underappreciated amplifier. Research on analogous gynecological procedures shows that women with higher pre-procedure anxiety scores consistently report more severe pain, even after accounting for the actual physical characteristics of the procedure.17PubMed. Impact of preprocedural anxiety levels on pain perception in patients undergoing office hysteroscopy Longer waiting times in the clinic before the test also correlated with higher pain scores in the same study. If you are scheduled for an HSG, taking an NSAID like ibuprofen beforehand, asking your clinic about topical or injectable local anesthesia, and minimizing the anxious wait time all seem to contribute to a better experience. Some clinics are testing virtual-reality headsets for distraction, though early evidence from related office procedures has not shown a clear benefit beyond placebo.18PubMed Central. Virtual reality for pain relief during office hysteroscopy: a randomized controlled trial
Complications and How to Reduce Them
Serious complications from HSG are uncommon, but three deserve attention: infection, contrast intravasation, and allergic reaction.
Pelvic inflammatory disease (PID) after HSG is the risk that gets the most discussion. In women with normal-looking tubes, the infection rate is extremely low, effectively approaching zero in one large retrospective series.19American Journal of Obstetrics & Gynecology. Efficacy of antibiotic prophylaxis in preventing pelvic inflammatory disease after hysterosalpingography The risk concentrates in women whose tubes are already dilated, suggesting pre-existing damage or chronic infection. In that subgroup, the PID rate was about 11% without antibiotics and dropped to zero with doxycycline prophylaxis in the same study. Guidelines from the Society of Obstetricians and Gynaecologists of Canada recommend prophylactic antibiotics for women found to have dilated tubes during the procedure.20Journal of Obstetrics and Gynaecology Canada. Antibiotic Prophylaxis in Obstetric and Gynaecologic Procedures A retrospective cohort study found that among all women undergoing HSG, antibiotic prophylaxis cut the overall PID rate from about 1.4% to 0.5%, with doxycycline being the most protective option.21PubMed. The effect of antibiotic prophylaxis for acute pelvic inflammatory disease after hysterosalpingography: a retrospective cohort study
Intravasation occurs when contrast dye enters the bloodstream through the uterine venous or lymphatic channels rather than staying in the uterine and tubal lumen. A systematic review covering over 19,000 HSG procedures found this happened in about 2.7% of oil-based procedures and 2.0% of water-based ones. Among those, actual oil embolism was rare: 18 cases out of more than 19,000 procedures, all without serious lasting consequences when fluoroscopy guidance was used properly. Four cases of serious harm (one retinal and three cerebral) were described in reports that did not mention adequate fluoroscopy guidance during the procedure.22PubMed. Safety of oil-based contrast medium for hysterosalpingography: a systematic review Real-time fluoroscopy is the key safeguard: the operator can see contrast entering blood vessels early and stop the injection before a significant volume embolizes.23PubMed. Intravasation during hysterosalpingography using oil-base contrast media
Thyroid Concerns with Oil-Based Contrast
One side effect that has received increasing scrutiny is the impact of oil-based iodinated contrast on thyroid function. Oil-based dyes like Lipiodol contain a high iodine load, and because they clear from the body slowly (over weeks to months rather than hours), the iodine exposure is prolonged. A prospective study tracking thyroid function in women after oil-based HSG found that iodine excess was almost universal, with 90% of participants having extremely elevated urinary iodine concentrations, and this excess persisted for at least three months in two-thirds of women. Subclinical hypothyroidism developed in 38% of participants, though the vast majority of those cases were mild.24The Journal of Clinical Endocrinology & Metabolism. The SELFI Study: Iodine Excess and Thyroid Dysfunction in Women Undergoing Oil-Soluble Contrast Hysterosalpingography A small number also developed overt or subclinical hyperthyroidism.
This finding matters because many of these women are trying to conceive, and untreated hypothyroidism during early pregnancy is associated with adverse outcomes. A review by the European Society of Urogenital Radiology concluded that while side effects of oil-based contrast are rare overall, thyroid dysfunction and peritoneal inflammation are genuine risks that deserve monitoring.25PubMed Central. Contrast media for hysterosalpingography: systematic search and review providing new guidelines by the Contrast Media Safety Committee of the European Society of Urogenital Radiology Clinics that use oil-based contrast are increasingly checking thyroid function after the procedure, particularly in women with a history of thyroid disease or positive thyroid antibodies. Water-based contrast, which clears quickly, does not carry this thyroid risk, which is one reason the choice between the two is not as simple as “oil is always better because it boosts fertility.”
Radiation Exposure in Context
Because HSG uses fluoroscopy and radiographic images, it delivers a dose of ionizing radiation to the pelvis, which understandably concerns women of reproductive age. The effective radiation dose from a typical HSG has been measured at roughly 1.2 to 2.5 mSv, depending on the facility and technique.26PubMed. Radiogenic risks from hysterosalpingography 27PubMed Central. Assessment of Patient Absorbed Radiation Dose during Hysterosalpingography: A Pilot Study in Southwest Nigeria For perspective, this is in the same ballpark as a CT scan of the head or a round-trip transatlantic flight. The estimated risk of causing a genetic anomaly in a future embryo was calculated to be less than one-thousandth of the background rate.28PubMed. Radiogenic risks from hysterosalpingography Doses can climb if the procedure is prolonged or if excessive radiographic exposures are taken, which is another argument for experienced operators using modern fluoroscopy equipment.
For women who want to avoid radiation entirely, ultrasound-based alternatives exist. Hysterosalpingo-contrast sonography (HyCoSy) and hysterosalpingo-foam sonography (HyFoSy) use saline or foam injected through the cervix while transvaginal ultrasound tracks its passage through the tubes. These methods avoid ionizing radiation and can be performed in an office setting, but they do not produce the same detailed image of the tubal lumen that fluoroscopy provides, and they lack the decades of validation behind conventional HSG.29PubMed. Evaluating Fallopian Tube Patency: What the Radiologist Needs to Know More importantly, ultrasound-based alternatives do not replicate the fertility-boosting effect seen with oil-based HSG, which for many patients is now part of the clinical rationale for choosing conventional HSG in the first place.
When HSG Is Not the Right Test
HSG is primarily a fertility-workup tool. It is not particularly useful for evaluating conditions that affect the muscle wall of the uterus (such as adenomyosis or intramural fibroids that do not impinge on the cavity), because the dye only outlines the interior surface. MRI and ultrasound are better choices for those situations.30PubMed. Infertility in women: diagnostic evaluation with hysterosalpingography and other imaging techniques Similarly, HSG cannot assess ovarian function, peritoneal endometriosis, or the state of the ovarian surface, all of which may matter for fertility but require different imaging or surgical evaluation.
There are also straightforward contraindications. HSG should not be done during active pelvic infection, during pregnancy, or immediately after uterine instrumentation such as a curettage. Women with a known severe iodine allergy need either premedication with corticosteroids and antihistamines or an alternative test. And because HSG involves fluoroscopy, it is scheduled to fall before ovulation to minimize any risk to a very early pregnancy that has not yet been detected.
For women whose primary question is the shape of the uterine cavity rather than tubal patency, office hysteroscopy is often the better choice. A thin camera inserted through the cervix gives a direct view of the cavity and allows the operator to biopsy or treat certain lesions at the same time. Pain management for hysteroscopy draws on similar principles to HSG: anxiety drives pain perception, local anesthesia helps, and procedure duration matters.31PubMed Central. Impact of anxiety levels on the perception of pain in patients undergoing office hysteroscopy But hysteroscopy cannot evaluate the tubes, so the two tests answer different questions and are often complementary rather than interchangeable.