Blood Clots, Endometriosis and Fibroids: What to Know

Seeing blood clots during your period can be unsettling. If you also live with endometriosis or uterine fibroids, it’s natural to wonder whether those clots are normal, a sign of heavy menstrual bleeding, or something more dangerous like a deep vein thrombosis (DVT). This guide explains what menstrual clots are, how endometriosis and fibroids contribute to heavy bleeding, when to seek care, and the safest treatment options—grounded in guidance from trusted sources such as the NIH, CDC, FDA, and ACOG.

What menstrual blood clots are—and aren’t

During menstruation, your body sheds the uterine lining. When bleeding is heavy, natural clotting can occur before blood leaves the uterus, forming gelatinous clots that can look dark red with tissue-like strands. Small, occasional clots—especially on the heaviest days—can be normal. However, frequent clots larger than a quarter, prolonged heavy bleeding, or symptoms of anemia (fatigue, dizziness, shortness of breath) warrant evaluation. The American College of Obstetricians and Gynecologists (ACOG) notes that soaking through a pad or tampon every hour for several hours is a sign to seek care for abnormal uterine bleeding.

Importantly, menstrual clots are different from dangerous blood clots in the veins (venous thromboembolism, or VTE), such as DVT or pulmonary embolism (PE). VTE clots form in blood vessels, not in the uterus, and cause symptoms like leg swelling and pain (DVT) or chest pain and shortness of breath (PE).

How fibroids and endometriosis contribute to clots

Uterine fibroids

Fibroids are benign growths of the muscle wall of the uterus. Submucosal or large intramural fibroids can disrupt the uterine lining and increase surface area, often causing heavy menstrual bleeding, passage of clots, pelvic pressure, and anemia. The NIH’s Office on Women’s Health highlights heavy or prolonged periods as a hallmark symptom of fibroids, especially when the uterine cavity is involved.

Endometriosis (and adenomyosis)

Endometriosis occurs when tissue similar to the uterine lining grows outside the uterus, causing inflammation and pain. Some people with endometriosis also experience heavy or irregular bleeding with clots, though pelvic pain is the most common symptom. Adenomyosis—when lining-like tissue grows into the uterine muscle—often coexists with endometriosis and is strongly linked to heavy bleeding and clots. NIH resources note that adenomyosis can cause severe cramps, enlarged tender uterus, and menorrhagia (heavy bleeding).

When to worry about dangerous clots (DVT/PE)

Most period clots are not dangerous blood clots. However, know the symptoms of VTE and seek urgent care if they occur:

• DVT: swelling, warmth, redness, and pain—usually in one calf or thigh
• PE: sudden shortness of breath, chest pain that may worsen with deep breaths, rapid heartbeat, coughing up blood

Risk factors for VTE include recent surgery or hospitalization, prolonged immobility (e.g., long flights), pregnancy and the postpartum period, smoking, obesity, some inherited clotting disorders, active cancer, and use of estrogen-containing medications. The CDC provides detailed information on DVT/PE symptoms and risk factors.

Getting evaluated: what to expect

Your clinician will ask about bleeding patterns, pain, fertility goals, and personal/family history of clots. Evaluation may include:

• Blood tests: complete blood count (to check for anemia) and iron studies; pregnancy test when appropriate
• Screening for bleeding disorders if heavy bleeding started at menarche or there’s a family history (e.g., von Willebrand disease)
• Pelvic ultrasound to assess for fibroids, adenomyosis, or ovarian cysts
• Consideration of endometriosis based on symptoms; sometimes laparoscopy confirms diagnosis, but many are treated based on clinical findings

Treatment options—and clot safety considerations

The best plan depends on your diagnosis, symptoms, clotting risk, and reproductive goals. Discuss the benefits and risks of each option with your clinician.

Supportive care

• Nonsteroidal anti-inflammatory drugs (NSAIDs) can reduce period pain and modestly decrease bleeding.
• Iron repletion (dietary changes and/or supplements) treats iron-deficiency anemia from heavy bleeding.

Non-hormonal medicine for heavy bleeding

• Tranexamic acid, an antifibrinolytic, can reduce menstrual blood loss on heavy days. Important safety note: Using tranexamic acid with estrogen-containing birth control may increase the risk of dangerous clots; the NIH’s MedlinePlus and FDA safety information advise against combining them unless specifically directed by a clinician.

Hormonal options

• Levonorgestrel-releasing intrauterine device (IUD) substantially reduces bleeding and cramping and is effective for many with fibroid-related heavy bleeding if the uterine cavity is not severely distorted.
• Progestin-only pills or injections can lighten periods and help with endometriosis-related pain.
• Combined estrogen-progestin methods (pills, patch, ring) can regulate cycles and reduce bleeding and pain, but they carry a small increased risk of VTE, especially in people with additional risk factors (e.g., smokers over 35, prior clots). Discuss your personal risk with your clinician and review FDA guidance.
• GnRH analogs and antagonists with add-back therapy: Short-term regimens can shrink fibroids and reduce bleeding and ease endometriosis pain. FDA-approved combinations include relugolix/estradiol/norethindrone acetate (Myfembree) for heavy menstrual bleeding due to fibroids and for endometriosis pain, and elagolix-based therapies. These products include boxed warnings about thromboembolic risk; careful screening for clot history and risk factors is essential.

Procedural and surgical options

• Myomectomy removes fibroids while preserving the uterus; best for those seeking future fertility.
• Uterine artery embolization (UAE/UFE) shrinks fibroids by blocking their blood supply; not recommended if pregnancy is desired.
• Radiofrequency ablation (e.g., Acessa, Sonata) treats fibroids with heat energy via minimally invasive approaches.
• Endometrial ablation reduces bleeding by treating the uterine lining; not for people who may want future pregnancies.
• Hysterectomy is definitive for fibroids and adenomyosis when other treatments fail or are not desired.
• For endometriosis, laparoscopic excision or ablation of lesions can relieve pain; add-back or maintenance hormonal therapy often helps prevent recurrence.

When to call a clinician—and when to go to the ER

• Schedule a visit if you pass frequent clots larger than a quarter, soak through pads/tampons hourly for several hours, have bleeding longer than 7–8 days, or develop anemia symptoms.
• Seek emergency care for signs of VTE: one-sided leg swelling/pain, sudden chest pain, shortness of breath, or coughing up blood.

Practical steps you can take now

• Track your cycles and bleeding (number of pads/tampons, size of clots, pain scores) to share with your clinician.
• Review your personal clotting risk (family/personal history, smoking status, recent surgery, immobilization) before starting estrogen-containing treatments.
• Ask about non-estrogen options if you have elevated VTE risk.
• Prioritize iron-rich foods and consider iron supplementation if advised.

With the right evaluation and a tailored plan, most people can control heavy bleeding and reduce clotting while minimizing clot-related risks.

Trusted resources

• NIH Office on Women’s Health: Uterine Fibroids — womenshealth.gov
• NIH Office on Women’s Health: Endometriosis — womenshealth.gov
• NIH Office on Women’s Health: Adenomyosis — womenshealth.gov
• ACOG: Abnormal Uterine Bleeding — acog.org
• CDC: DVT/PE Facts — cdc.gov
• CDC: Bleeding Disorders and Heavy Periods — cdc.gov
• NIH MedlinePlus: Tranexamic Acid Safety — medlineplus.gov
• FDA: Myfembree (relugolix/estradiol/norethindrone) safety info — fda.gov

This article is for educational purposes and is not a substitute for personal medical advice. Always consult a qualified clinician about your symptoms and treatment options.