What causes fibroids?

Nathaniel Scharping
Anna Funk
Uterine fibroids are common — and understudied. Here’s what’s known about fibroids, including what causes them, and how to best treat them.

What You Need to Know About Fibroids

A fibroid diagnosis can be scary. The uterine tumors can be painful, and not much is known about where they come from and what causes fibroids to grow. Up to 80% of women and people with a uterus will get fibroids at some point in their life¹, yet a surprising number of people haven’t heard of them. In some cases, doctors may opt to remove the uterus entirely to treat fibroids. But today, a growing number of treatment options mean there are many less-invasive options for treatment.

What are fibroids?

Fibroids are benign tumors that grow on the walls of your uterus. Medical professionals sometimes refer to them as leiomyomas or myomas. A lot of people that have fibroids don’t even know they have them, and that’s fine — it’s the symptoms they cause that can become problematic. 

Fibroids are frustratingly understudied, as are so many reproductive health issues. Even today, the most common fibroid treatment offered to patients is simply cutting out the uterus entirely, despite the availability of other options.² Another prime example: The system for classifying fibroids was developed in 1918, and hasn’t been updated since.³ 

What causes fibroids?

Researchers know surprisingly little about what causes fibroids to grow. So far, it seems like a complex combination of factors are at play. Research has found links between fibroids and:

  • Hormones. Studies have found that people who use hormonal birth control that includes estrogen and progesterone, like The Pill and hormonal IUDs, are 20% less likely to have fibroids.⁴ Other researchers have proposed that exposure to endocrine-disrupting chemicals — pollutants that mess with your hormones — increase risk.⁵ 
  • Genes. If you have a close relative with fibroids, your risk is much higher. Researchers have identified a myriad of genes that can increase your likelihood for fibroids. Factors that can mess with your DNA, called epigenetics, also can make them more likely.⁶
  • Age. The odds of developing fibroids rise as you approach menopause. Most people with fibroids are first diagnosed in their 30s or 40s, and the risk of fibroids is highest when you’re in your 50s.⁷ After menopause, the risk drops off and fibroids may even shrink and disappear, thanks to the hormonal changes happening in your body.

A number of studies have linked fibroids to other factors, such as:

The majority of these studies are small, and still need to be repeated in larger, more controlled settings before we can understand how important they really are.

Researchers have found that Black women get fibroids three times more often than white women, and that when they do, they get them at a younger age, they’re larger, their symptoms are more severe, and their risk of complications is higher.¹¹ The reason why Black women get fibroids more often is still a medical mystery, but some researchers suspect it relates to genetics and underlying health conditions. The lack of attention on the issue is just one of many examples of long-running racial disparities in the healthcare system and beyond. 

What are the symptoms?

Fibroids don’t always cause symptoms, and a lot of people who have them don’t even know they’re there. But for some, they can cause a wide range of troubles, including:

  • pelvic or lower back pain
  • heavy periods characterized by more bleeding than is normal for you
  • increased urination or incontinence
  • a feeling of fullness in the abdomen
  • pain during intercourse
  • pregnancy complications or infertility

It’s important to see your ob-gyn if you think you might have fibroids. Some fibroid symptoms can feel similar to those caused by ovarian cysts and endometriosis. These other conditions need different treatments, so it’s important to get an accurate diagnosis to alleviate your symptoms.

Doctors can check for fibroids during your routine pelvic exam. If they need to take a closer look, they might bring in heavy machinery, like ultrasound machines or MRIs. 

What’s the best treatment for fibroids?

Luckily, fibroids don’t typically pose a big danger if they’re dealt with properly, and there are a wide range of treatment options available. If your symptoms are minimal, your doctor might even recommend leaving them alone. They call this “watchful waiting.” This fibroid treatment, or non-treatment, is an especially common practice for older people, since fibroids often shrink and disappear after menopause.

If fibroids are causing you pain or other symptoms, your doctor will likely recommend treatment, which ranges from non-invasive medication to surgical removal. Here are some of the most common fibroid treatment options.

Hormonal treatments for fibroids

There’s some evidence that hormonal contraceptives, like the pill and certain intrauterine devices (IUDs) can help manage some fibroid symptoms like heavy bleeding.¹² Some studies have also shown that the hormones progesterone and estrogen affect fibroid growth.¹³ Doctors may prescribe drugs that change how these hormones are produced or transmitted in the body to alleviate symptoms and shrink fibroids. 

Gonadotropin-releasing hormone (GnRH) analogs

A class of drug called gonadotropin-releasing hormone (GnRH) analogs mimic hormones in the body to simulate the onset of menopause.¹⁴ Research shows it’s a reliable way to shrink fibroids, but side effects of the drug, like bone loss, makes it a bad option for long-term use. Doctors most often prescribe GnRH drugs temporarily, for instance to shrink fibroids before a surgery to remove them completely.  

Removing fibroids

When fibroids are causing problems, like interfering with your ability to have children, your doctor may recommend procedures to remove or destroy the growths. One option is to use focused ultrasound to heat and destroy fibroid cells, often guided by an MRI. Doctors may also recommend uterine artery embolization, in which they inject tiny particles into the arteries that supply blood to the uterus.¹⁵ Slowing the blood flow kills the fibroids while leaving the other tissues in the uterus intact.

Surgeons can directly cut out fibroids, too, which is called a myomectomy. To do this surgery, doctors create a small incision and use small, flexible tools to cut out the growths. This procedure comes with minimal risks, but it’s not a permanent solution — fibroids can grow back over time.

For years, doctors have most commonly recommended hysterectomies as treatment for symptomatic fibroids — removing the uterus entirely.² It’s effective, but it’s the most extreme option. Removing a uterus is a major surgery that comes with long recovery times, can come with complications, and eliminates a person’s ability to have children.

Some people feel emotionally connected to their uterus, even without a desire to have children, and prefer not to part with it. So although a hysterectomy may be the right choice for some people, it’s not something you should feel pressured into. It’s typically best to have an open conversation with your doctor about the alternatives.

Closing the research gap

Scientists agree that fibroids need more study.¹⁶ As with other aspects of reproductive health, we’re still waiting on good, solid science to show us what causes fibroids and how we can best treat and prevent them. Some of that work is underway now, but we have a long way to go before we close this portion of the medical research gap.

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