Fibroids grow in and around the uterus, and their exact position within the uterine wall determines what symptoms they cause, how they affect fertility, and which treatments work best. They are classified by their relationship to two layers of the uterus: the inner lining (endometrium) and the outer surface (serosa). This gives rise to three main categories, with several subtypes based on how deeply a fibroid sits within the muscular wall.
The Three Main Fibroid Locations
The muscular wall of the uterus, called the myometrium, is the tissue where fibroids originate. Depending on which direction they grow, they fall into one of three groups.
Intramural fibroids are the most common type. They grow entirely within the muscular wall, surrounded on all sides by uterine muscle, with no contact with the inner lining or the outer surface. As they enlarge, they can stretch the uterus and make it feel bigger than normal. Because they’re embedded in the wall itself, they often go unnoticed until they grow large enough to cause heavy periods or a sense of pelvic fullness.
Submucosal fibroids grow toward the inside of the uterus, pressing into or bulging through the inner lining. Some are mostly buried in the wall with only a small portion poking into the cavity. Others dangle entirely inside the cavity on a narrow stalk, like a grape hanging from a vine. These are the least common type, but they tend to cause the most noticeable bleeding symptoms because they directly disrupt the lining where menstrual blood forms.
Subserosal fibroids grow in the opposite direction, pushing outward from the uterus toward the pelvic cavity. Some are mostly embedded in the wall with just a bulge on the surface. Others project almost entirely outside the uterus, connected by a stalk. These stalked (pedunculated) subserosal fibroids carry a risk of twisting on their blood supply, which can cause sudden, sharp pain. Large subserosal fibroids can also press on nearby organs like the bladder or bowel.
How Deep a Fibroid Sits Matters
Gynecologists use a standardized numbering system from the International Federation of Gynecology and Obstetrics (FIGO) to pinpoint exactly where a fibroid falls on the spectrum from fully inside the cavity to fully outside the uterus. The scale runs from 0 to 8:
- Type 0: Completely inside the uterine cavity, attached by a stalk
- Type 1: Mostly in the cavity, with less than half its diameter in the wall
- Type 2: Bulges into the cavity, but more than half sits within the wall
- Type 3: Entirely within the wall but touching the inner lining without distorting it
- Type 4: Entirely within the wall, no contact with inner lining or outer surface
- Type 5: Mostly in the wall, with a bulge on the outer surface
- Type 6: Mostly projecting from the outer surface, with less than half in the wall
- Type 7: Entirely outside the uterus, attached by a stalk
- Type 8: Located in the cervix or detached from the uterus entirely
This numbering isn’t just academic. It directly shapes the conversation about treatment, because a Type 0 fibroid can typically be removed through the vagina with a thin camera, while a Type 5 or 6 requires a completely different surgical approach through the abdomen.
Less Common Locations
A small number of fibroids grow outside the main body of the uterus. Cervical fibroids account for roughly 0.6% of all fibroids and develop in the narrow lower portion of the uterus that opens into the vagina. Their position makes them surgically challenging because the bladder sits in front, the rectum behind, and the tubes that carry urine from the kidneys (ureters) run along either side. The most common symptom of cervical fibroids is abnormal bleeding, reported in about 44% of cases, followed by pressure-related complaints and pelvic pain.
Even rarer are “parasitic” fibroids, which have detached from the uterus entirely and developed their own blood supply from nearby tissue in the pelvis. These sometimes begin as pedunculated subserosal fibroids that twist, separate, and reattach to other structures like the broad ligament, the sheet of tissue that drapes over the uterus and fallopian tubes.
How Location Shapes Symptoms
Two fibroids of identical size can produce completely different symptoms depending on where they sit. A fibroid growing toward the front of the uterus presses against the bladder, which can trigger frequent urination or a constant feeling of needing to go. One growing toward the back puts pressure on the bowel, potentially causing constipation. Submucosal fibroids that distort the inner lining are the primary drivers of heavy menstrual bleeding and prolonged periods, even when they’re relatively small.
Intramural fibroids that don’t touch the lining or outer surface often produce no symptoms at all until they reach a significant size. At that point, the uterus itself enlarges, and many women describe a feeling of fullness or bloating in the lower abdomen. Multiple intramural fibroids scattered through the wall can make the uterus irregular in shape, which sometimes becomes noticeable during a routine pelvic exam.
Location and Fertility
Submucosal fibroids have the strongest negative effect on the ability to conceive and carry a pregnancy. Research pooling data across multiple studies found that submucosal fibroids reduced implantation rates by roughly 60 to 70% and nearly quadrupled the risk of miscarriage compared to women without fibroids. Clinical pregnancy rates dropped by more than half. Removing submucosal fibroids consistently improves these outcomes, which is why their removal is generally recommended before fertility treatment.
Intramural fibroids also appear to reduce fertility, though the effect is smaller. A large meta-analysis covering over 9,000 IVF cycles found that even intramural fibroids that don’t distort the cavity reduced live birth rates by about 19% and increased miscarriage risk by 27%. The question of whether to remove intramural fibroids before fertility treatment is less clear-cut and depends on their size and proximity to the lining. Subserosal fibroids, growing away from the cavity, have the least impact on reproductive outcomes.
How Fibroid Location Is Mapped
Transvaginal ultrasound is the first-line imaging tool because it’s widely available and relatively inexpensive. It works well for confirming that fibroids are present and measuring the ones it can see. However, it’s highly dependent on the skill of the person performing the scan, and it misses a significant number of smaller fibroids. In one study comparing imaging to actual surgical findings, ultrasound detected only 40% of fibroids that were confirmed when the uterus was examined directly.
MRI is considerably more accurate. The same study found that MRI detected 80% of confirmed fibroids, with a positive predictive value of 91%, and its size measurements were closer to the real dimensions, off by about half a centimeter on average compared to three-quarters of a centimeter for ultrasound. MRI is particularly valuable when a surgeon needs a precise map before planning a procedure, because it can clearly show how deeply a fibroid extends into the wall, whether it contacts the inner lining, and how it relates to surrounding structures. The tradeoff is cost and availability, so MRI is typically reserved for complex cases or when ultrasound findings are unclear.
How Location Determines Treatment Approach
Submucosal fibroids that project into the uterine cavity (Types 0 and 1) are candidates for hysteroscopic removal, where a surgeon passes a thin instrument through the vagina and cervix to reach the fibroid directly. This approach works best for fibroids smaller than 4 centimeters that aren’t deeply embedded in the wall. Recovery is typically quick, with most women returning to normal activities within a few days.
Fibroids that are intramural or subserosal generally require a laparoscopic or robotic-assisted approach, where the surgeon works through small incisions in the abdomen. Most myomectomies can be performed this way, even for large fibroids. Open abdominal surgery, which involves a larger incision and longer recovery, is reserved for cases with many fibroids or very large ones where the surgeon needs to feel through the uterine wall to locate them all. Uterine artery embolization, which shrinks fibroids by cutting off their blood supply, is another option for bulky subserosal fibroids pressing on adjacent organs.
The key point is that there’s no single best treatment for fibroids. The right approach depends almost entirely on where the fibroids sit, how many there are, how large they’ve grown, and what symptoms or fertility goals are driving the decision.