Myomas, also called uterine fibroids, are not dangerous in the vast majority of cases. They are benign (non-cancerous) tumors made of smooth muscle cells that grow in or on the uterus, and in premenopausal women, over 99.7% are benign. That said, fibroids can cause serious problems depending on their size, location, and number, and a small number of situations do require urgent medical attention.
Why Most Myomas Are Not a Cancer Risk
Fibroids grow from the smooth muscle of the uterine wall, primarily in response to estrogen. They are the most common benign gynecologic tumor, and the odds that a presumed fibroid is actually a cancerous growth called a leiomyosarcoma are very low. For women under 50, the chance is roughly 1 in 770. That risk increases with age: for women over 60, it rises to about 1 in 65. Pathologists distinguish the two by examining cell behavior under a microscope, looking at how fast cells are dividing and whether there is abnormal cell death within the tissue.
Because the cancer risk is so low in younger women, a fibroid diagnosis alone is not a reason to panic. Most fibroids are discovered incidentally during a routine ultrasound and never cause symptoms at all.
When Fibroids Do Cause Problems
The real danger from myomas is not cancer. It’s the complications they can create as they grow. The most common of these is heavy menstrual bleeding, which over months or years can drain your iron stores and lead to iron-deficiency anemia. In severe cases, this anemia can become life-threatening. Case reports document women with fibroid-related bleeding reaching critically low hemoglobin levels, well below what the body needs to carry oxygen safely. If your periods have become significantly heavier, longer, or more frequent, or if you feel constantly exhausted, pale, or short of breath, those are signs your fibroids may be causing meaningful blood loss.
Large fibroids can also press on nearby organs. A fibroid sitting against the bladder can make you feel like you need to urinate constantly. One pressing on the rectum can cause constipation or a persistent feeling of pressure. These symptoms are uncomfortable and disruptive, but they’re mechanical problems caused by the fibroid’s size, not signs of something more sinister.
Acute Pain and Emergency Situations
Most fibroids grow slowly and cause gradual symptoms, but there are scenarios where they create sudden, severe pain. One is called degeneration: when a fibroid outgrows its blood supply, the tissue begins to die. This is most common during pregnancy, particularly in the second and third trimesters, and especially in fibroids larger than 5 centimeters. The result is intense, localized abdominal pain that can last days.
A rarer but more urgent situation is torsion. Some fibroids grow on a stalk that hangs off the outside of the uterus. If that stalk twists, it cuts off blood flow to the fibroid, causing sudden sharp pain, often in the lower abdomen, sometimes with vomiting. Torsion is uncommon, but it requires emergency surgical treatment because the tissue will die without blood supply and can cause serious complications if left untreated.
Effects on Fertility and Pregnancy
If you’re trying to get pregnant, the location of a fibroid matters more than its size. Fibroids that grow into or distort the uterine cavity, called submucosal fibroids, have the most significant impact on fertility. They can physically block sperm from reaching an egg, prevent an embryo from reaching the uterus, or interfere with implantation by compressing the uterine lining. Research shows that women with cavity-distorting fibroids have significantly lower implantation rates, lower pregnancy rates, and higher miscarriage rates. These fibroids also disrupt the normal wave-like contractions of the uterus that help move sperm and embryos, and they alter the expression of key proteins in the uterine lining that are needed for successful implantation.
The encouraging news is that removing submucosal fibroids appears to restore reproductive potential. Fibroids that sit on the outer surface of the uterus or deep within the muscle wall without distorting the cavity have a much smaller, and sometimes negligible, effect on fertility.
During pregnancy, fibroids are associated with elevated risks of preterm birth, cesarean delivery, placenta previa (where the placenta covers the cervix), placental abruption (early separation of the placenta), postpartum hemorrhage, and breech presentation. Larger fibroids carry higher risks for several of these complications. Pain is the single most common fibroid-related problem during pregnancy, particularly in the second and third trimesters.
Size and Treatment Thresholds
Not every fibroid needs treatment. Many women live with fibroids their entire reproductive years and never need intervention. Treatment typically becomes a conversation when fibroids cause symptoms that affect your quality of life: heavy bleeding, significant pain, pressure symptoms, or fertility problems.
Size plays a role in surgical decisions. For minimally invasive removal, some guidelines suggest fibroids up to 15 centimeters if there’s only one, or up to three fibroids each 5 centimeters or smaller. When there are more than five fibroids or they exceed 10 to 15 centimeters, the surgery becomes more complex, often requiring longer operating times and multiple incisions in the uterus. These thresholds vary by surgeon and situation, so the decision is individualized.
Fibroids tend to shrink after menopause as estrogen levels drop, which is why watchful waiting is sometimes a reasonable approach for women nearing that transition.
Signs That Need Attention
Most fibroids sit quietly and pose no real threat. But certain symptoms signal that yours may be causing harm. Periods heavy enough to soak through a pad or tampon every hour, bleeding that lasts longer than seven days, or passing large clots all point to blood loss that could lead to anemia. Sudden severe abdominal pain, especially if it comes on quickly and doesn’t let up, could indicate torsion or degeneration. Rapid growth of a known fibroid, particularly after menopause when fibroids should be shrinking, warrants closer evaluation to rule out the rare possibility of a malignant tumor. And if you’re experiencing difficulty getting pregnant or recurrent miscarriages, fibroids distorting your uterine cavity may be contributing.