Hysterosalpingogram (HSG)

A hysterosalpingogram (HSG) is an X-ray test of the uterus and fallopian tubes. The clinician passes a contrast dye through the cervix into the uterus and tubes. The dye appears on fluoroscopy, a live X-ray image.¹ The test provides a real-time image of the shape of the uterus. It also shows tubal patency, whether the tubes are open.² HSG is one of the most common tests of tubal patency in a fertility evaluation.³

HSG shows filling defects, gaps in the dye, and changes in the outline of the uterus. These findings can point to growths inside the uterus, such as polyps, submucosal fibroids, and adhesions (scar tissue).⁴ HSG shows a uterine septum, a wall that divides the uterus.⁵ It also shows a tube blocked near the uterus or near its far end (proximal or distal tubal obstruction).⁶

Identifying a growth inside the uterus often requires hysteroscopy, 3D ultrasound, or saline sonography, an ultrasound with saline in the uterus.⁴ MRI is reserved for complex Mullerian anomalies, differences in how the uterus formed. It is used when 3D ultrasound cannot resolve the question. For most uterine septal defects, 3D ultrasound is now the preferred test.⁵

HSG has limits. A tube in spasm can appear blocked when it is open (a false positive).⁶ HSG fills only the uterus and the inside of the tubes. For this reason, it cannot detect endometriosis on the pelvic lining. It also cannot detect pelvic adhesions, scar tissue in the pelvis. Those conditions require laparoscopy for assessment.⁶ A complete evaluation of a couple requires more than a dye study.

Does the HSG itself improve fertility? Clinicians have long observed that some couples conceive in the months after an HSG, especially when oil-based dye is used.⁷ Randomized trials have reported higher pregnancy rates after an oil-based HSG than after a water-based one. The mechanism by which oil-based dye improves fertility is unknown.⁸ Proposed mechanisms include immune effects of the iodized oil, a flushing effect (mechanical clearance), and surfactant action.⁹

The purpose of an HSG is to find a structural cause. This added benefit does not replace a cause-based evaluation of why conception has not yet occurred.

In a cause-based evaluation, HSG is often an early step in assessing the tubes.³ Diagnostic laparoscopy, an examination of the pelvis through a camera, may follow. It can give a clear answer about pelvic disease.¹⁰ When a standard HSG shows a blockage near the uterus, the next step is to determine whether the blockage is true or caused by spasm.

Selective salpingography places a catheter at the opening of one tube and images that tube alone. It confirms a true blockage or reveals a false positive from spasm.¹¹ In some cases, the test confirms a true partial blockage near the uterus. In that case, transcervical catheterization of the fallopian tubes can open it. A catheter and guidewire pass through the blockage, often in the same session, without open surgery.