Uterine fibroids (also known as myomas or leiomyomas) are muscular growths that form in the walls of your uterus. They are surprisingly common, affecting anywhere from 20% to 50% of people with a uterus. The vast majority of uterine fibroids are benign, or non-cancerous, and do not impact your risk for developing uterine cancer.
Uterine fibroids vary in size
Uterine fibroids vary widely in terms of size. Many of them are pea-sized or smaller and nearly impossible to see or feel during a pelvic exam.
Although rare, uterine fibroids can grow to the size of a softball and cause uncomfortable symptoms and complications.
Uterine fibroids and uterine polyps aren't the same
Uterine fibroids should not be confused with uterine polyps. Polyps are precancerous growths made up of the same tissue that lines your uterus (the endometrium), while fibroids are made of muscle and connective tissues.
The two conditions do share symptoms, so polyps may be mistaken for fibroids. The best way to know for sure is to get an accurate diagnosis from your doctor.
Causes and types of uterine fibroids
What causes uterine fibroids?
Experts don’t know exactly what causes uterine fibroids. Multiple factors likely play a role in their development and growth.
Hormones. While we don’t know the exact cause of fibroids, we do know that hormones play a big role. Fibroid cells appear to be directly controlled by hormones – specifically estrogen and progesterone. They may even have more estrogen and progesterone receptors than normal muscle cells. This is why you’re more likely to develop fibroids during your reproductive years and as you approach menopause (perimenopause), times when these hormones fluctuate the most.
It is also why uterine fibroids tend to grow during pregnancy, which brings about high progesterone levels, and shrink following menopause, when your body stops producing high levels of estrogen and progesterone.
Genetic changes. Many fibroids contain genes that differ from those of the normal muscle cells in the uterus. These differences might be what causes uterine fibroids to develop and grow.
There is evidence that uterine fibroids run in families, meaning there is likely a genetic component to them.
Types of uterine fibroids
There are also several types of uterine fibroids, depending on their location:
- Intramucosal fibroids (intramural fibroids). These fibroids grow within the muscular layer of the uterine wall.
- Pedunculated fibroids. These fibroids grow on stems that can project into the uterine cavity or outside of the uterus. They can look like mushrooms.
- Submucosal fibroids. This type of fibroid grows into the uterine cavity. Because of this, they are more like to cause uncomfortable symptoms like heavy menstrual bleeding and an increased risk of infertility or miscarriage.
- Subserosal fibroids. This type of fibroid grows on the outside of the uterus. They are more likely to press on nearby organs like the bladder and rectum, causing uncomfortable symptoms like frequent urination or rectal pain.
Symptoms of uterine fibroids
Most uterine fibroids do not cause symptoms, so you may have a fibroid without realizing it. Often, fibroids are discovered during a regular pelvic exam or an ultrasound during pregnancy.
If you do have symptomatic fibroids, however, it can be very uncomfortable. Common symptoms include:
- A firm mass is detected, often near the middle of the pelvis. Your healthcare provider may be able to feel this during a pelvic exam.
- Bleeding between periods (intermenstrual bleeding).
- Frequent urination. This happens when the fibroid (often a subserosal fibroid) presses against the bladder.
- Heavy menstrual bleeding or lengthy periods.
- Leg pain.
- Lower back pain.
- Pain during intercourse.
- Pelvic pain. This happens when a fibroid presses on pelvic organs.
- Rectal pain. This happens when a fibroid (usually a subserosal fibroid) presses against the rectum.
- Rarely, reproductive problems like infertility.
Who is at risk for developing uterine fibroids?
A risk factor is anything that increases your chance of developing a condition. Risk factors for uterine fibroids include:
- A diet that is high in red meat and low in fiber, fruits, and vegetables.
- Being of African-American heritage.
- Family history. If a close relative has had uterine fibroids, you are more likely to develop them yourself.
- High blood pressure.
- Perimenopause. This is the period when your body is transitioning towards menopause. It usually happens around age 40, and it is marked by hormone fluctuations that may contribute to fibroid growth.
Just because you are at risk for uterine fibroids does not mean you will develop them. However, you should talk to your doctor about your risks and pay attention to any symptoms you’re feeling.
Diagnosing uterine fibroids
Fibroids are most often found during a routine pelvic exam. Your healthcare provider may feel a firm, painless lump on the uterus. They may want to perform additional tests, which can include:
- Blood tests. This is to check for iron deficiency anemia, which is a common symptom of uterine fibroids that cause heavy bleeding.
- Imaging exams. These tests allow your doctor to see your uterus and any fibroids or irregular tissue.
- Hysterosalpingography. This is an X-ray exam of the uterus and fallopian tubes that uses dye. This is often done if you are concerned about infertility to rule out blocked fallopian tubes.
- Hysteroscopy. In this test, your doctor inserts a small, flexible tube with a camera at the end (hysteroscope) that allows them to see inside your uterus.
- MRI. This test uses a large magnet, radio waves, and a computer to make 2-D images of an internal organ or structure.
- Ultrasound. This is an ultrasound test using a small tool (transducer) that is pressed against your belly or placed in the vagina. The ultrasound uses high-energy sound waves to produce an image of your uterus on a screen.
- X-ray. Beams of energy make images of bones and internal organs on film.
Endometrial biopsy. If your doctor sees any suspicious tissue during an imaging exam, they may want to take a small sample, or a biopsy, for further examination. The tissue sample will be removed using a small tube inserted into the uterus. The tissue is then examined in a lab for signs of cancer or other problems.
Treatments for uterine fibroids
Treatment for uterine fibroids depends on the size, location, and type of thyroid, as well as your symptoms and goals. If you have uterine fibroids that aren’t causing symptoms, you may not need any treatment. Fibroids are rarely cancerous, slow-growing, and usually shrink after menopause, so your doctor might recommend just keeping an eye on things. This is known as “watchful waiting.”
If your symptoms are mild but manageable, your doctor might recommend taking non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen. These pain medications are effective for mild pain associated with uterine fibroids, although they won’t lessen symptoms like heavy menstrual bleeding.
Medications cannot cure fibroids. However, certain hormone medications can help regulate symptoms like heavy menstrual bleeding and may even be able to shrink your fibroids.
- Gonadotropin-releasing hormone agonists(GnRHa). These medications temporarily block the production of estrogen and progesterone and cause you to enter a menopause-like state. This, in turn, can cause your uterine fibroids to shrink. You may experience side effects like hot flashes and depression, so your doctor will likely prescribe GnRH agonists only for a few months. Sometimes, you may take GnRHa to shrink fibroid tumors before surgery.
- Hormonal intrauterine device (IUD). Hormonal IUDs like Mirena release small amounts of progestin, which has the same effects as progesterone, directly into the uterus. This helps relieve symptoms like heavy menstrual bleeding, but it does not shrink fibroids. Hormonal IUDs are also a very effective form of birth control.
- Iron supplements. Heavy bleeding caused by fibroids can cause anemia, a condition where your blood can’t carry enough oxygen. Your doctor may prescribe iron supplements to help manage this. Be sure to follow your doctor’s instructions when taking iron, since taking iron tablets incorrectly can cause unpleasant side effects like nausea and diarrhea.
- Tranexamic acid. These medications reduce menstrual bleeding by preventing newly-formed blood clots from breaking down. You only need to take them during heavy bleeding days.
If your fibroids are causing severe symptoms or do not respond well to medications, your doctor may recommend surgery. There are many different types of surgery available to remove or shrink fibroids. They include:
- Endometrial ablation. This procedure involves removing the uterine lining (the endometrium) to reduce heavy bleeding long-term. It can be done using radiofrequency, hot water, freezing, a metal loop, or other methods. However, you will not be able to get pregnant after endometrial ablation.
- Hysterectomy. A hysterectomy is a surgery to remove your uterus. It is the only permanent way to remove fibroids and prevent the development of others, but it is a major surgery that comes with risks. You may be a candidate for a hysterectomy if your uterine fibroids are very large or widespread, if your symptoms are severe, if less invasive treatments have been unsuccessful, and if you are past or near menopause. After a hysterectomy, you will not be able to get pregnant.
- MRI-guided focused ultrasound surgery (MRgFUS). Despite its name, this is a non-invasive procedure: you will not have any incisions or scarring. Instead, you will be inside an MRI machine that has a specific ultrasound wand (transducer) used for treatment. Your doctor will use the MRI to precisely locate the fibroid and then use focused, high-energy soundwaves (sonication) to heat and destroy some of the fibroid tissue—while sparing healthy tissue.
- Uterine artery embolization (UAE, or sometimes uterine fibroid embolization). In this procedure, your doctor will thread a thin, flexible tube (a catheter) through one of the large arteries in your leg and guide it to the fibroid. They will then inject embolic agents, gel-like particles that cut off the fibroid’s blood supply. This will cause the fibroid to shrink. In rare cases, embolization can cause problems with the blood supply going to the ovaries, so UAE is better suited for people who do not want to have children in the future.
- Myomectomy. This is surgery to remove fibroids from the uterine wall. Depending on the size and location of the fibroid, this can be laparoscopic (making very few incisions and using a viewing tool) or it may require a more traditional approach. You and your doctor will discuss which surgical approach is right for you. In a myomectomy, the uterus stays in place, meaning that you will be able to become pregnant if you want to. However, surgically removing fibroids does not prevent others from developing. You should continue to get regular checkups and monitor your symptoms.
- Radiofrequency ablation. Your surgeon will make a few, small incisions in your abdomen and insert a small viewing instrument and an ultrasound. They will use the viewing tool to find the fibroid and then use the ultrasound tool to heat and damage the fibroid or the blood vessels that feed it. After the surgery, the fibroid will shrink on its own, and symptoms will lessen.
About uterine fibroids and pregnancy
If you are diagnosed with uterine fibroids, you may be concerned about how it could impact your fertility or pregnancy. In many cases, uterine fibroids are benign and cause no problems during pregnancy.
However, a submucosal fibroid – the type that grows into the uterine cavity – can cause infertility, pregnancy complications, or even miscarriage. Additionally, pregnancy causes many hormonal changes that can feed fibroid growth.
In general, the most common complications seen with uterine fibroids during pregnancy are:
- C-section (Cesarean section). If you are pregnant and have fibroids, you are more likely to need a C-section than someone without fibroids.
- Placenta previa. This is a condition in which the placenta (the organ that gives your baby oxygen and nutrients) covers the cervix. This means you likely can’t have a vaginal birth and are at increased risk that the placenta will rupture or bleed.
- Preterm delivery. If a fibroid grows significantly, it can place pressure on the uterus and cause contractions before your due date. Preterm delivery can be harmful to your baby since their lungs and other organs are still developing.
- Breech position. Uterine fibroids that limit the space in your uterus can cause your baby to be breech, meaning they are bottom down instead of head down. This may require that you have a C-section.
Pregnancy complications are scary. But, by working with your healthcare providers and closely monitoring your pregnancy, you should be able to manage complications and come up with a birth plan that meets your needs.
If you are trying to become pregnant and are at risk for uterine fibroids, you may want to talk to your doctor about your risks and options.
The Office on Women’s Health (OWH). Uterine fibroids (https://www.womenshealth.gov/a-z-topics/uterine-fibroids)
MedlinePlus: National Library of Medicine. Uterine fibroids (https://medlineplus.gov/ency/article/000914.htm)
National Institute of Child Health and Human Development (NICHD). Uterine Fibroids (https://www.nichd.nih.gov/health/topics/uterine)