Have you been diagnosed with endometriosis and then discovered fibroids on an ultrasound? It is completely understandable to wonder whether one condition caused the other.

So, does endometriosis cause fibroids?

Not exactly. Endometriosis is not currently proven to directly cause uterine fibroids. They are two different gynecological conditions with different characteristics. However, they can occur in the same person, and newer research suggests that women with endometriosis may have a higher likelihood of also having fibroids.

That distinction matters. An association is a signal that two conditions occur together more often than expected; it is not proof that one condition creates the other.

Let’s look at what the evidence actually tells us—and how you can tell endometriosis and fibroids apart.

Does Endometriosis Cause Fibroids?

The best current answer is no, not as a proven cause-and-effect relationship.

Endometriosis involves tissue similar to the lining of the uterus growing outside the uterus. Fibroids, on the other hand, are benign growths that develop from the muscle tissue of the uterus. In other words, they are different diseases arising in different ways.

But there is an important twist.

A 2025 systematic review and meta-analysis published in EClinicalMedicine looked at 23 studies involving 3,109,231 women. It found that women with endometriosis had approximately 2.9 times higher odds of having uterine fibroids than women without endometriosis. In an analysis using asymptomatic controls, the association was even stronger. However, the researchers rated the overall certainty of evidence as low, partly because the studies differed considerably.

So, should we say endometriosis causes fibroids? No.

A more accurate interpretation is that endometriosis and fibroids appear to be associated and may coexist more often than previously recognized.

Both conditions are also influenced by hormonal and biological factors, which may partly explain why they sometimes appear together. But researchers are still working to understand the precise relationship.

What Is Endometriosis?

Endometriosis is a chronic gynecological condition in which tissue similar to the lining of the uterus grows outside the uterus, often around the ovaries, fallopian tubes and pelvic lining. It can also affect the bowel, bladder and other pelvic structures.

Because these lesions respond to hormonal changes during the menstrual cycle, they can trigger inflammation, pain and scar tissue called adhesions.

What Are Uterine Fibroids?

Fibroids, also called leiomyomas or myomas, are benign growths that develop from the muscle tissue of the uterus. They can grow inside the uterine cavity, within the uterine wall, on the outer surface, or on a stalk.

Some fibroids cause no symptoms at all. Others can become a significant source of bleeding, pressure or reproductive problems.

Endometriosis vs Fibroids: What’s the Difference?

At first glance, endometriosis and fibroids can look like two versions of the same problem. Both can cause painful periods, pelvic discomfort and fertility concerns.

But they are not the same.

Feature	Endometriosis	Fibroids
What is it?	Tissue similar to the uterine lining growing outside the uterus	Benign growths from uterine muscle
Typical location	Ovaries, pelvic lining, bowel, bladder and other sites	Inside, within or on the outside of the uterus
Pain	Often significant and may occur beyond menstruation	Depends on size and location
Heavy bleeding	May occur	Very common symptom
Pain during sex	Common	Can occur
Fertility	Can be affected	Can be affected, particularly with certain fibroid locations
Cancer	Endometriosis is not cancer	Fibroids are benign

ACOG notes that both endometriosis and fibroids can contribute to painful periods, but their underlying conditions are distinct.

Symptoms They Have in Common

Here is where things get confusing.

Both conditions may cause:

• Pelvic pain
• Painful periods
• Heavy menstrual bleeding
• Pain during sex
• Fertility problems

That overlap means you cannot reliably diagnose either condition simply by matching symptoms to an online checklist.

How Their Symptoms Differ

Endometriosis is often associated with pain that follows the menstrual cycle but can extend beyond the period, including pain with bowel movements, urination or sex. Fibroids are more commonly associated with heavy or prolonged menstrual bleeding and pressure symptoms, although pain can occur too.

Endometriosis Pain vs Fibroid Pain

A useful way to think about it is location.

With endometriosis, pain can result from inflammation, bleeding from lesions and adhesions affecting nearby pelvic structures.

With fibroids, symptoms often depend on where the fibroid sits, how large it is and whether it distorts the uterus.

Neither pattern is absolute, however. Real patients do not always follow textbook examples.

Can You Have Endometriosis and Fibroids at the Same Time?

Yes.

This is one of the most important things to understand when researching endometriosis vs fibroids.

Having one does not protect you from having the other. In fact, the latest evidence suggests the two conditions may occur together more frequently than previously appreciated. The 2025 meta-analysis found a significant association between endometriosis and fibroids across a very large population.

Why does this matter?

Because overlapping conditions can create overlapping symptoms. Imagine trying to identify two different songs playing at the same time. Some sounds blend together, making it difficult to know which one is responsible for what you are hearing.

The same can happen with pelvic pain or heavy periods.

You might have fibroids causing heavy bleeding and endometriosis contributing to severe pelvic pain. Treating only one problem may therefore leave some symptoms unresolved.

Which Is Worse: Endometriosis or Fibroids?

This is one of the most common questions—and there is no medically correct answer that applies to everyone.

Neither endometriosis nor fibroids is automatically “worse.”

Severity depends on factors such as the extent of disease, location of lesions or fibroids, symptoms, complications, fertility plans and response to treatment.

Mayo Clinic’s gynecology experts similarly note that the two conditions can share symptoms and affect fertility, but they progress differently.

When Endometriosis Can Be More Severe

Endometriosis can become particularly challenging when it causes:

• Severe or persistent pelvic pain
• Extensive adhesions
• Endometriomas involving the ovaries
• Deep disease involving the bowel or bladder endometriosis
• Significant impact on fertility or quality of life

The NHS notes that severe endometriosis may require specialist treatment and, in some circumstances, surgery.

When Fibroids Can Cause More Problems

Fibroids may become particularly troublesome when they:

• Cause very heavy menstrual bleeding
• Contribute to iron-deficiency anemia
• Grow large enough to create pelvic pressure
• Compress the bladder or bowel
• Distort the uterine cavity
• Interfere with fertility or pregnancy in selected cases

So rather than asking, “Which disease is worse?” a more useful question is:

“Which condition is causing my symptoms, and how extensive is it?”

That is the question a thorough gynecological assessment needs to answer.

Can Endometriosis and Fibroids Affect Fertility?

Yes, both can affect fertility, but the mechanisms are different.

Endometriosis can affect the ovaries and fallopian tubes, contribute to adhesions and inflammation, and alter the pelvic environment. The NHS recognizes endometriosis as a potential cause of fertility problems because of its effects on the reproductive organs.

Fibroids can also affect fertility in some women. Their effect depends heavily on their size and location. Fibroids that distort the uterine cavity may interfere with implantation, while larger fibroids can sometimes affect the anatomy of the reproductive tract.

And when both conditions are present, it becomes even more important to look at the entire picture rather than focusing on one scan finding.

How Are Endometriosis and Fibroids Diagnosed?

Diagnosis begins with your symptoms and medical history—not just a scan.

Your gynecologist may ask when your pain occurs, how heavy your periods are, whether you have pain during sex or bowel movements, and whether pregnancy is an immediate or future goal.

Ultrasound and MRI

Ultrasound is commonly used to identify fibroids and can also help identify certain forms of endometriosis.

MRI can provide additional information about pelvic anatomy and may be particularly useful when deep endometriosis or complex fibroid disease is suspected. The NHS lists ultrasound and MRI among investigations used when endometriosis is suspected.

When Laparoscopy May Be Considered

Laparoscopy is a minimally invasive procedure in which a small camera is introduced through a small incision in the abdomen.

It can be used to directly inspect the pelvis and, in appropriate situations, treat endometriosis during the same procedure.

The important point is that a normal scan does not automatically mean there is no endometriosis. Diagnosis needs to be interpreted alongside symptoms and clinical findings.

How Are Endometriosis and Fibroids Treated?

Treatment should never be based on the diagnosis alone. The right approach depends on symptoms, disease extent, age, overall health and—very importantly—whether you want to become pregnant.

Treatment for Endometriosis

Treatment can include pain medication, hormonal therapy and surgery when appropriate. Hormonal treatment may help control symptoms, while endometriosis surgery can be considered when symptoms are severe, medical treatment has not worked or fertility is affected.

For extensive or deep endometriosis, treatment may require greater surgical expertise, particularly when the bowel, bladder or ureters are involved.

Treatment for Fibroids

Fibroids do not always need treatment.

If they are small and causing no symptoms, monitoring may be all that is necessary. When treatment is required, options can include medication, procedures to shrink or remove fibroids, and surgery.

A myomectomy removes fibroids while preserving the uterus, making it an important consideration for some women who want to maintain fertility.

When Minimally Invasive Surgery May Be Appropriate

Laparoscopic and robotic techniques can provide less invasive approaches for selected cases of endometriosis and fibroids.

Dr. Lucas Minig’s gynecological practice in Valencia focuses on individualized management of conditions including endometriosis and uterine fibroids, with minimally invasive laparoscopic and robotic surgery among the treatment approaches available for appropriate patients. His practice also emphasizes establishing the diagnosis first and discussing complex cases within a multidisciplinary setting.

That philosophy is particularly relevant when endometriosis and fibroids occur together: the goal should not simply be to remove something visible on a scan, but to understand which findings are actually responsible for your symptoms and reproductive concerns.

When Should You See a Gynecologist?

Do not assume severe period pain is something you simply have to tolerate.

Consider seeing a gynecologist if you have:

• Period pain that interferes with work, school or everyday activities
• Very heavy or prolonged periods
• Persistent pelvic pain
• Pain during sex
• Pain when passing urine or stool, particularly around your period
• Difficulty becoming pregnant
• Symptoms that are worsening despite treatment

The NHS advises seeking medical evaluation when endometriosis symptoms affect daily life or continue despite initial treatment.

An accurate diagnosis can be the difference between repeatedly treating symptoms and actually addressing the underlying condition.

Conclusion

So, does endometriosis cause fibroids? Based on current evidence, there is no established proof that endometriosis directly causes fibroids. They are separate gynecological conditions, but they can occur together, and a 2025 systematic review found that fibroids were significantly more common among women with endometriosis.

The bigger lesson is not to get trapped in an “endometriosis or fibroids” mindset. Sometimes the answer is both. And when symptoms overlap—especially pelvic pain, heavy bleeding or fertility problems—a careful assessment can help determine what is actually happening.

If you are dealing with persistent or complex symptoms, a gynecologist experienced in endometriosis and fibroid management can help distinguish the conditions and build a treatment plan around your health and fertility goals. In Valencia, Dr. Lucas Minig’s practice provides individualized care for both endometriosis and uterine fibroids, including minimally invasive laparoscopic and robotic approaches when clinically appropriate.

FAQs

Can fibroids turn into endometriosis?

No. Fibroids do not transform into endometriosis. They are different conditions with different biological characteristics. However, a person can have both at the same time.

Can endometriosis and fibroids be treated together?

They can sometimes be managed during the same overall treatment plan, but the approach depends on the location and severity of each condition. In selected patients, minimally invasive surgery may address fibroids and endometriosis as part of a carefully planned procedure.

Is endometriosis more painful than fibroids?

Not necessarily. Endometriosis can cause severe chronic or cyclical pelvic pain, while fibroids can cause pain, cramping and significant pressure. The severity of either condition varies from person to person.

Can fibroids and endometriosis cause infertility?

Yes, both can contribute to fertility problems, although the mechanisms differ. Endometriosis can affect the ovaries, fallopian tubes and pelvic environment, while certain fibroids—particularly those that distort the uterine cavity—can interfere with fertility.

Can an ultrasound tell whether I have endometriosis or fibroids?

Ultrasound can often identify fibroids and may detect certain types of endometriosis, but it cannot always rule out endometriosis. Depending on your symptoms and suspected disease, your doctor may consider MRI or, in selected circumstances, laparoscopy.