A hysterosalpingogram, often referred to as an HSG, is a specialized X-ray procedure used to evaluate the internal structure of the uterus and the condition of the fallopian tubes. This test is frequently performed as a preliminary step in a fertility workup to investigate potential anatomical causes of difficulty conceiving. A normal result provides reassurance that the reproductive pathway is unobstructed, allowing focus to shift to other potential factors.
What is an HSG and Why is it Performed
The hysterosalpingogram procedure involves injecting a liquid contrast dye through the cervix, which then fills the uterine cavity and flows into the fallopian tubes. Specialized X-ray imaging, known as fluoroscopy, captures a series of images as the dye moves through these structures. The primary diagnostic goal of the HSG is to assess two specific anatomical features: the shape and contour of the uterine cavity and the patency, or openness, of the fallopian tubes. Structural issues within the uterus, or blockages in the tubes, are significant causes of infertility. By confirming that the pathways are clear, the HSG helps guide subsequent treatment and testing.
The Characteristics of a Normal Uterine Cavity
A healthy uterine cavity, when fully filled with contrast dye during an HSG, displays a distinct and characteristic shape on the X-ray image. This cavity is typically smooth and triangular or pear-shaped, with the wider base at the top where the fallopian tubes connect and the narrow apex pointing down toward the cervix. The dye should fill the space evenly, creating a clear and well-defined outline.
A normal result shows a smooth internal lining without any disruption to the flow or contour of the contrast agent. The absence of “filling defects” is a specific indicator of a normal cavity. Filling defects can suggest conditions like endometrial polyps, submucosal fibroids, or intrauterine scar tissue (adhesions).
Interpreting Normal Fallopian Tube Patency
The most telling feature of a normal HSG result is the demonstration of fallopian tube patency. As the dye flows from the uterus, it should smoothly enter the narrow openings of both fallopian tubes, tracing their delicate, fine-line structure across the image. A normal tube appears as a slender, continuous line of contrast extending away from the uterus.
The definitive confirmation of patency is the “peritoneal spill” of the contrast agent. This occurs when the dye travels completely through the tube and visibly diffuses, or spills, out of the fimbriated end into the surrounding abdominal cavity. This spillage confirms that the tube is open from the uterine connection all the way to its distal end. A fully normal result requires this free spillage to be demonstrated on both the left and right sides of the pelvis.
Next Steps After Receiving a Normal Result
A normal HSG result effectively rules out tubal factor infertility, meaning blocked fallopian tubes are not the cause of difficulty conceiving. This outcome allows the diagnostic workup to move on to evaluating other potential causes, such as issues with ovulation, egg quality, or sperm analysis. A clear HSG streamlines the process by eliminating a major anatomical concern.
A normal HSG is sometimes followed by a temporary increase in the chance of conception, an effect often called “therapeutic flushing.” The mechanical action of the dye flushing through the tubes may clear minor debris or mucous plugs that were not causing a complete obstruction. While the HSG is primarily a diagnostic tool, this potential flushing effect may slightly enhance the chance of pregnancy in the months immediately following the procedure.