Uterine fibroids are often discovered by accident during a routine pelvic exam, before any symptoms appear. When a doctor suspects fibroids or needs to confirm them, the diagnostic process typically moves from a physical exam to ultrasound imaging, with more specialized tests added only when the picture isn’t clear enough to guide treatment.
The Pelvic Exam
A pelvic exam is usually the first step. Your doctor places two gloved fingers inside the vagina while pressing down on your abdomen with the other hand. This allows them to feel the size, shape, and contour of your uterus. Fibroids can make the uterus feel irregularly shaped, enlarged, or lumpy rather than smooth and pear-sized. Many fibroids are first noticed this way, during a routine visit with no symptoms at all.
A pelvic exam can raise suspicion, but it can’t confirm fibroids on its own. It also can’t tell your doctor how many fibroids you have, exactly where they’re located, or how large they are. For that, imaging is needed.
Ultrasound: The Standard First Test
Ultrasound is the go-to imaging tool for diagnosing fibroids. On an ultrasound screen, a fibroid typically appears as a solid, round, well-defined mass within the muscular wall of the uterus, often casting a characteristic shadow at its edges. Most women will have one of two types of ultrasound, and sometimes both in the same visit.
A transabdominal ultrasound uses a probe on the outside of your abdomen. You’ll need to drink at least 24 ounces of clear fluid about an hour beforehand and avoid emptying your bladder. The full bladder pushes the uterus into a better position and moves bowel loops out of the way, giving the technician a clearer view. This approach works well for getting a big-picture look at the uterus, but image quality can be limited if you carry more weight around your midsection.
A transvaginal ultrasound uses a smaller probe inserted into the vagina, getting much closer to the uterus. For this one, you’ll empty your bladder right before the procedure. Transvaginal scans are more sensitive for detecting small fibroids because the probe sits just centimeters from the uterus. However, if your uterus is very large or tilted backward, the top of the uterus may fall outside the probe’s field of view.
Neither type of ultrasound requires fasting or sedation. The whole process typically takes 15 to 30 minutes.
How Accurate Is Ultrasound?
Ultrasound is very good at ruling fibroids out when they aren’t there, with a specificity of 95%. Its sensitivity for detecting fibroids that do exist is lower, around 47% in one study that used hysteroscopy as the reference standard. This means ultrasound rarely gives a false alarm, but it can miss fibroids, particularly small ones or those growing into the uterine cavity. When symptoms don’t match what the ultrasound shows, your doctor may recommend additional imaging.
MRI for a More Detailed Picture
MRI is considered the best imaging method for mapping fibroids precisely. It shows the exact number, size, and location of every fibroid in the uterus, including details that ultrasound can miss. Your doctor is most likely to order an MRI in a few specific situations: when the ultrasound results are unclear, when it’s hard to tell whether a pelvic mass is a fibroid or something else, when the uterus is too large for ultrasound to capture completely, or when surgery or a procedure like uterine artery embolization is being planned.
MRI is also particularly useful for distinguishing fibroids from adenomyosis, a condition where tissue similar to the uterine lining grows into the muscular wall. These two conditions can look similar on ultrasound and cause overlapping symptoms like heavy bleeding and pelvic pressure, but they require different treatment approaches. On MRI, fibroids appear as distinct round masses with clear borders, while adenomyosis tends to show up as a diffuse thickening of the uterine wall without a defined edge.
Saline Infusion Sonography
Standard ultrasound can struggle with fibroids that bulge into the uterine cavity (called submucosal fibroids), which are the type most likely to cause heavy bleeding and fertility problems. Saline infusion sonography, sometimes called a sonohysterogram, solves this by filling the uterine cavity with sterile saline before scanning. The fluid separates the walls of the uterus and outlines any masses protruding into the cavity, making them much easier to see and measure.
This test also helps classify how much of the fibroid sits inside the cavity versus embedded in the wall, a detail that directly affects whether a fibroid can be removed through the cervix or requires abdominal surgery. In a study comparing saline infusion sonography to hysteroscopy (the gold standard), the two methods agreed on fibroid classification in 92% of cases when most of the fibroid was inside the cavity, and 75% when most of the fibroid was embedded in the wall.
Hysteroscopy: A Direct Look Inside
Hysteroscopy is the only diagnostic method that lets a doctor see the inside of the uterus directly. A thin, lighted scope is passed through the cervix into the uterine cavity, which is gently expanded with fluid so the entire lining can be inspected. The procedure can be done in an office or outpatient setting and typically doesn’t require general anesthesia.
Hysteroscopy is most useful when submucosal fibroids are suspected, when other imaging has been inconclusive, or when your doctor wants to evaluate the cavity before fertility treatment. It can also be used to take a tissue sample if there’s any question about whether a growth is a fibroid or something else. In some cases, small fibroids can be removed during the same procedure, turning a diagnostic step into a treatment.
Blood Tests
Blood tests don’t diagnose fibroids themselves, but they’re a routine part of the workup when fibroids are suspected or confirmed. A complete blood count checks for anemia, which is common in women with fibroids that cause heavy or prolonged periods. Chronic blood loss from fibroids can gradually deplete your red blood cells and iron stores, sometimes severely. Identifying anemia matters because it may need to be treated before any fibroid procedure, and because the degree of anemia helps your doctor gauge how much the fibroids are affecting your health overall.
What the Diagnosis Process Looks Like in Practice
For most women, the path is straightforward: a pelvic exam raises the question, an ultrasound answers it, and blood work checks for anemia. That combination is enough to diagnose fibroids and start discussing treatment options in the majority of cases. MRI, saline infusion sonography, and hysteroscopy come into play when the situation is more complex, such as when fibroids are numerous, very large, in tricky locations, or when distinguishing them from other conditions matters for treatment planning.
The type of testing your doctor recommends depends largely on your symptoms and what decisions need to be made next. If you have no symptoms and fibroids were found incidentally, you may not need any further testing at all. If you’re dealing with heavy bleeding, pelvic pain, or fertility concerns, more detailed imaging helps pinpoint which fibroids are responsible and what treatment options are realistic.