Intramural fibroids are almost always benign growths, and most people who have them will never experience a serious health threat. That said, they can cause problems depending on their size, number, and exact position within the uterine wall. The real question isn’t whether intramural fibroids are inherently dangerous, but whether yours are large enough or positioned in a way that could lead to complications worth monitoring.
What Intramural Fibroids Are
Intramural fibroids grow within the muscular wall of the uterus. They’re the most common type of fibroid. Some sit deep in the muscle, completely surrounded by uterine tissue. Others grow closer to the inner lining of the uterus, where they can press against or distort the uterine cavity. That distinction matters because fibroids that push into the cavity tend to cause more symptoms, particularly heavier bleeding and fertility issues, than fibroids buried entirely within the wall.
Cancer Risk Is Extremely Low
This is usually the first worry, so here’s the short answer: the chance that a growth presumed to be a fibroid is actually cancerous is roughly 2 in 1,000. In a study of nearly 1,400 women who had surgery for suspected fibroids, only three turned out to have leiomyosarcoma, the rare cancer that can mimic a fibroid. Among women under 40, the rate was zero. The risk increased slightly in women over 49, reaching about 1.2%, but even then, the overwhelming majority of fibroids are benign.
Heavy Bleeding and Anemia
The most common way intramural fibroids cause real harm is through chronic heavy menstrual bleeding. Over months or years, losing more blood each cycle than your body can replace leads to iron-deficiency anemia. Mild anemia causes fatigue, dizziness, and shortness of breath. Severe anemia from fibroids, while uncommon, can become life-threatening. Case reports document women with hemoglobin levels dropping below 2.0 g/dL (normal is roughly 12 to 16 g/dL for women), a point where the heart can no longer compensate and organ failure becomes a risk.
Most people never reach that extreme. But if your periods are soaking through a pad or tampon every hour, lasting longer than seven days, or leaving you exhausted, those are signs your bleeding has crossed from inconvenient to medically significant. A simple blood test can check your iron levels and hemoglobin.
Pressure on Nearby Organs
As intramural fibroids grow, they can press on surrounding structures. The specific symptoms depend on which direction the fibroid expands:
- Bladder pressure: Frequent urination, urgency, or difficulty fully emptying your bladder.
- Bowel pressure: Constipation, bloating, or in rare cases involving very large fibroids, bowel obstruction.
- Vein compression: Large fibroids can compress pelvic veins, occasionally causing swelling in the legs.
These symptoms tend to develop gradually as fibroids enlarge, and they’re more common with fibroids that grow to 5 centimeters or larger. Bowel obstruction and significant vein compression are rare and typically only happen with very large or multiple fibroids.
How They Affect Fertility
Intramural fibroids can reduce your chances of getting pregnant, even when they don’t visibly distort the uterine cavity. A large meta-analysis of 28 studies covering over 9,000 IVF cycles found that women with non-cavity-distorting fibroids had about a 14% lower clinical pregnancy rate and a 19% lower live birth rate compared to women without fibroids. Miscarriage rates were about 27% higher.
The picture is somewhat muddied, though. A stricter analysis that controlled for age and used more rigorous methods to confirm fibroid type found no significant difference in live births or miscarriage rates. This suggests the effect may be smaller than headline numbers imply, and that the size and precise location of the fibroid matter more than simply having one.
If you’re trying to conceive and have intramural fibroids, the key factor is whether the fibroid is pushing into or distorting the uterine cavity. Fibroids that indent the cavity are more likely to interfere with embryo implantation and are more often considered for removal before fertility treatment.
Fibroids and Pregnancy Complications
Fibroids during pregnancy have been linked in older studies to a roughly 60% increase in miscarriage risk, with some estimates as high as threefold. However, a well-designed prospective study that adjusted for confounding factors like age and health status found no increased miscarriage risk for intramural fibroids specifically (adjusted hazard ratio of 1.05, essentially no difference from women without fibroids).
Other pregnancy complications associated with fibroids in general include preterm birth, placental abruption (where the placenta separates from the uterine wall early), fetal malpresentation (the baby not being head-down), and higher rates of cesarean delivery. These risks tend to scale with fibroid size and number rather than being a universal consequence of having any fibroid at all. Many women with small intramural fibroids have uncomplicated pregnancies.
How Fast They Grow
Fibroids are unpredictable growers. The median growth rate is about 9% in volume every six months, but individual fibroids range wildly, from shrinking by nearly 90% to growing by 138% in that same period. About a third of fibroids experience growth spurts, defined as a 30% or greater increase in volume over three months. Larger fibroids tend to grow faster, with the biggest fibroids in one study increasing by a median of 35% per year.
This variability is why periodic monitoring with ultrasound makes sense, particularly if you have symptoms. A fibroid that’s small and stable may never need treatment. One that’s growing rapidly warrants closer attention, partly to manage symptoms and partly because unusually fast growth in a postmenopausal woman (when fibroids should be shrinking) can occasionally prompt further evaluation to rule out rare cancerous changes.
When Intramural Fibroids Become a Problem
Most intramural fibroids don’t require treatment. They become a concern when they cause heavy enough bleeding to produce anemia, grow large enough to compress your bladder or bowel, cause significant pelvic pain or pressure, or interfere with fertility. The threshold is functional: if a fibroid is changing your quality of life or your health markers, it’s worth addressing. If it’s sitting quietly in the uterine wall and you only know about it because it showed up on an unrelated scan, it typically needs nothing more than occasional monitoring.
Treatment options range from medications that reduce bleeding and shrink fibroids temporarily to procedures that cut off the fibroid’s blood supply or remove it surgically. The best approach depends on your symptoms, whether you want to preserve fertility, and the size and number of fibroids involved.