Endometriosis vs. Fibroids: What They Are

Endometriosis occurs when tissue similar to the endometrium (the uterine lining) grows outside the uterus—often on the ovaries, fallopian tubes, pelvic peritoneum, or, rarely, the bowel or bladder. These implants respond to hormones, which can trigger inflammation, scarring, and pain. The National Institutes of Health (NIH) estimates that about 10% of reproductive-age women have endometriosis.

Uterine fibroids (leiomyomas) are noncancerous growths of the muscle wall of the uterus. They vary in size and number and may grow within the uterine cavity (submucosal), within the wall (intramural), or on the outside surface (subserosal). The NIH notes that 20%–80% of women develop fibroids by age 50, with higher prevalence and symptom burden among Black women.

Are They Dangerous?

Neither condition is usually life-threatening. However, both can cause substantial health problems if untreated.

Endometriosis

• Chronic pain and organ damage: Inflammation and scarring can lead to severe pelvic pain, painful periods, painful sex, and sometimes bowel or urinary symptoms. Adhesions can affect pelvic organs and, in rare cases, lead to bowel obstruction or ureteral blockage.
• Fertility: Endometriosis is linked to reduced fertility in some individuals due to inflammation, scarring, and altered pelvic anatomy.
• Cancer risk: The National Cancer Institute notes a small increase in risk of certain ovarian cancers (clear cell and endometrioid types) in people with endometriosis. The absolute risk remains low.

Fibroids

• Heavy menstrual bleeding and anemia: Fibroids, especially submucosal ones, can cause heavy periods leading to iron-deficiency anemia, fatigue, and reduced productivity.
• Bulk symptoms: Large fibroids may cause pelvic pressure, abdominal distension, constipation, urinary frequency, or back pain.
• Pregnancy impact: Depending on size and location, fibroids can raise the risk of miscarriage, preterm birth, breech presentation, or cesarean delivery.
• Cancer risk: Fibroids are benign. A rare cancer called leiomyosarcoma can occur in the uterus, but leading authorities (e.g., ACOG) state it is not believed to arise from preexisting fibroids.

Symptoms: Where They Overlap—and Differ

Symptoms can look similar, which is one reason diagnosis can be delayed.

• Shared symptoms: Pelvic pain, painful periods, painful intercourse, bloating, and fertility challenges.
• Endometriosis-leaning clues: Severe pain that worsens around menstruation, pain with bowel movements or urination during periods, chronic pelvic pain, and sometimes pain even outside the menstrual window.
• Fibroid-leaning clues: Heavy or prolonged periods (needing to change protection hourly), passing clots, pelvic pressure or a “full” feeling, visible abdominal enlargement, and urinary frequency.

How Doctors Diagnose Each Condition

History and exam: A detailed symptom history and pelvic exam are first steps for both conditions.

Imaging: Pelvic ultrasound is the primary test for fibroids and can show their size and location. MRI is sometimes used for complex cases or treatment planning. Endometriosis may not be visible on ultrasound unless there’s an endometrioma (ovarian cyst); MRI can help in selected cases.

Definitive diagnosis of endometriosis: Laparoscopy with visualization and, when needed, biopsy remains the gold standard, though many clinicians treat based on symptoms and imaging when surgery isn’t immediately indicated.

Treatment Options Backed by Evidence

Endometriosis

• Pain control: NSAIDs may help menstrual pain.
• Hormonal therapy: Combined oral contraceptives, progestins (including levonorgestrel-releasing IUD), and GnRH modulators can reduce pain by suppressing hormonal cycling. The FDA has approved elagolix (Orilissa) for endometriosis pain, and a relugolix combination (Myfembree) for endometriosis-associated pain as well.
• Surgery: Laparoscopic excision or ablation of endometriosis lesions can improve pain and may help fertility in selected patients. Advanced disease sometimes requires multidisciplinary care.
• Supportive care: Pelvic floor physical therapy, heat, exercise, and cognitive behavioral strategies may complement medical therapy.

Fibroids

• Watchful waiting: If symptoms are mild, periodic monitoring may be appropriate.
• Medical therapy: NSAIDs for pain; iron for anemia; hormonal options (combined pills, progestins, levonorgestrel IUD) can reduce bleeding. Nonhormonal tranexamic acid is another option for heavy menstrual bleeding. The FDA has approved elagolix/estradiol/norethindrone acetate (Oriahnn) and relugolix/estradiol/norethindrone acetate (Myfembree) for heavy menstrual bleeding due to fibroids.
• Procedures: Uterine artery embolization (UAE) shrinks fibroids by cutting off their blood supply; MRI-guided focused ultrasound is a noninvasive option for select cases; myomectomy removes fibroids while preserving the uterus; hysterectomy is definitive for those not desiring future pregnancy.
• Fertility considerations: Submucosal fibroids are most strongly linked to infertility and miscarriage; myomectomy may improve outcomes in certain scenarios. Discuss fertility goals with a specialist before procedures like UAE.

Fertility and Pregnancy

Both conditions can affect reproductive outcomes, but many people conceive and carry healthy pregnancies with appropriate care.

• Endometriosis: May reduce fertility; fertility-focused surgery, ovulation induction, or assisted reproductive technologies (e.g., IVF) can be effective depending on the case.
• Fibroids: Effects depend on number, size, and location. Submucosal fibroids are most impactful. Preconception counseling can help tailor treatment.

When to Seek Care—And When It’s Urgent

See a healthcare professional if pelvic pain, heavy bleeding, or fertility concerns are affecting your life. Seek urgent care if you experience any of the following:

• Heavy bleeding soaking through a pad or tampon every hour for several hours
• Severe pelvic or abdominal pain with fever, vomiting, or fainting
• Signs of anemia (chest pain, shortness of breath, dizziness)
• Difficulty urinating, severe constipation, or new bowel/bladder incontinence

Bottom Line

Endometriosis and fibroids are usually not dangerous in a life-threatening sense, but they can seriously impact comfort, fertility, and daily functioning. The good news: evidence-based treatments—ranging from medical therapy to minimally invasive procedures—can control symptoms and protect long-term health. Partner with a clinician to tailor a plan that fits your goals, whether that’s pain relief, lighter periods, preserving fertility, or definitive treatment.

This article is for educational purposes and is not a substitute for professional medical advice. Always consult your healthcare provider about your specific situation.

Trusted Sources

• NIH NICHD – Endometriosis: https://www.nichd.nih.gov/health/topics/endometri/conditioninfo
• NIH NICHD – Uterine Fibroids: https://www.nichd.nih.gov/health/topics/uterine/conditioninfo
• National Cancer Institute – Endometriosis and Cancer Risk: https://www.cancer.gov/about-cancer/causes-prevention/risk/hormones/reproductive-history-fact-sheet#endometriosis
• U.S. Food and Drug Administration (FDA) – Orilissa (elagolix) for endometriosis pain: https://www.accessdata.fda.gov/drugsatfda_docs/label/2018/210450s000lbl.pdf
• FDA – Oriahnn (elagolix/estradiol/norethindrone) for fibroid-related bleeding: https://www.accessdata.fda.gov/drugsatfda_docs/label/2020/213382s000lbl.pdf
• FDA – Myfembree (relugolix/estradiol/norethindrone) for fibroids and endometriosis: https://www.accessdata.fda.gov/drugsatfda_docs/label/2023/214846s006lbl.pdf
• ACOG Patient FAQ – Uterine Fibroids: https://www.acog.org/womens-health/faqs/uterine-fibroids