Endometriosis Blood Clots: Causes, Symptoms, and When to Get Help

Often, when people hear the term “blood clots,” they think of the type of clots that form in arteries and veins that can lead to heart attack and stroke. But “blood clots” can also describe clot-like material that passes from the uterus and vagina during menstruation.

“Menstrual clots are part of the body’s response to bleeding,” says Gouri Pimputkar, DO, clinical lead at Allara Health. “Menstrual clots are clots in the sense that they are activated by the same clotting cascade to control endometrial bleeding during periods.The location and the circumstance in which they are formed is the difference.” 

Most people who menstruate experience menstrual blood clots, but people with endometriosis may have larger, more frequent clots. While heavy bleeding and clots can be part of living with endometriosis, it’s important to take your symptoms seriously and rule out other potential causes. Treating your endometriosis can also help reduce your symptoms. 

What are menstrual blood clots?

In a typical menstrual cycle, the endometrium, or lining of the uterus, thickens to support a pregnancy. If you don’t get pregnant that cycle, the lining breaks down and exits the body as menstruation, or your period. Menstrual blood clots are jelly-like masses that occur when the shedded uterine lining and blood sit and coagulate, or thicken, at the base of the uterus before exiting the body.  

Clots are most common during the heaviest days of your period, when your body cannot produce enough anticoagulants, a blood-thinning substance, to keep up with the bleeding. Period clots are also more common after long periods of rest, after sitting for hours or sleeping at night, when blood tends to pool. Clots, like period blood, range in color based on how quickly they leave your body. Clots that pass quickly are more likely to be a deep or bright red, while those that stay within the uterus longer tend to appear brown or dark red. 

Having a few small clots during your period is normal. Having many clots, or clots larger than the size of a quarter is often a sign of heavy menstrual bleeding. The amount of blood loss during the average period is two to three tablespoons. Those who have heavy menstrual bleeding, about one in five people who menstruate, tend to lose more than twice as much. Having heavy bleeding, and larger, more frequent clots, are common among those who have endometriosis. 

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Does endometriosis cause menstrual blood clots?

Experiencing large or frequent period blood clots can be a sign of endometriosis. There are many ways endometriosis can increase the likelihood of menstrual blood clots. 

Heavy bleeding

Endometriosis can cause heavy bleeding, which increases the likelihood of menstrual blood clots. When your lining sheds faster than it can exit your body, your body doesn’t have enough time to produce enough blood thinners to break down the tissue. And if this tissue sits and pools within the uterus, it’s more likely to form large clots. 

Faster rates of clotting 

People with endometriosis, especially endometriomas, a type of ovarian cyst often found in cases of deep-infiltrating endometriosis, have faster rates of clotting. Endometriosis lesions contain more platelets, a type of blood cell responsible for clotting, and people with endometriosis tend to have higher fibrinogen levels, a type of protein found in the blood that enables clotting. 

Inflammation 

Endometriosis is an inflammatory condition where cells similar to the lining of the uterus grow elsewhere in your body. These abnormal, displaced cells often grow on other pelvic organs like the ovaries, bladder, exterior of the uterus, and within the pelvis itself. 

Inflammation can increase the likelihood and speed at which blood clots. It can also increase the risk of bleeding and organ dysfunction. 

Uterine issues 

Changes within the uterus or to the pelvic anatomy caused by adhesions, a type of scar tissue common in people with endometriosis, can increase the likelihood of blood pooling and clots forming. 

Other uterine conditions that can co-occur with endometriosis can also cause period clots. Uterine growths like fibroids and polyps can change the anatomy of your uterus and cause bleeding irregularities. So can adenomyosis, a common condition among those with endometriosis that also causes severe cramping and heavy bleeding. 

Hormonal imbalances 

Endometriosis can cause estrogen dominance, where estrogen levels are high compared to progesterone levels. When these levels are imbalanced the uterine lining can become abnormally thick. This can lead to heavy bleeding and clotting when progesterone levels drop and you get your period. 

How endometriosis can cause menstrual clots

• Increased clotting: Faster production of clotting factors 
• Heavy bleeding: Not enough time for anticoagulants to thin shedded lining
• Hormonal imbalances: Estrogen dominance can thicken the endometrium 
• Inflammation: Increases the risk of bleeding and organ dysfunction
• Uterine issues: Related conditions like adenomyosis, fibroids, and polyps

What size or frequency of period blood clots is concerning?

Period blood clots typically accompany heavy menstrual bleeding. Small, infrequent blood clots are normal. Frequent clots or having multiple clots larger than a quarter (about an inch), may warrant further investigation.  

It can be hard to know whether your period is “normal,” if you’ve only ever experienced “abnormal” symptoms. A normal menstrual cycle typically ranges from 24 to 38 days. And the average period lasts 2 to 7 days, with anywhere from five to 80 mL of blood loss. Anything outside of these ranges is considered abnormal uterine bleeding. 

In addition to passing frequent or large clots, heavy periods may look like: 

• Needing to change your tampon or pad every two hours or less
• Consistently soaking through your pad or tampon 
• Having to wake up and change your pad or tampon
• Lengthy periods that last more than seven days 
• Bleeding that limits your ability to leave the house or maintain your normal routine

“While there is no magic number or size of clots that can be of concern, continued passage of clots associated with pain or heavy bleeding should be evaluated for underlying causes,” Pimputkar says.  

If you have severe cramping and pass one very large clot that is triangular, flesh colored or a pinkish-red, you may have experienced  a decidual cast. Decidual casts are rare, but typically a benign finding; they can be a side effect of certain hormone-based medications used to treat endometriosis. 

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When to seek emergency care

It’s important to reach out to your healthcare provider if your period lasts longer than seven days, especially if you have signs of heavy menstrual bleeding. Your healthcare provider can run tests and determine whether you need medication to help stop or slow your flow. 

If you feel lightheaded or fatigued, it may be a sign of anemia, an iron-deficiency that can result from excessive blood loss. Seek urgent care if you pass out or experience shortness of breath as it may be a sign of dangerously low blood pressure caused by excessive blood loss.  

Passing large clots paired with heavy bleeding can also be a sign of miscarriage. If you are pregnant or think you might be pregnant and are bleeding, contact your healthcare provider or seek emergency care. 

What other conditions can cause heavy clotting?

Endometriosis is not the only condition that can cause abnormal bleeding. “Clots and heavy bleeding can be related to structural issues with the uterus such as polyps, fibroids, adenomyosis, or even pre-cancer and cancer,” says Pimputkar. “The most common reason for heavy bleeding and clots is usually irregular ovulation from hormonal disturbances, such as PCOS.” 

Conditions that cause heavy bleeding and period blood clots include: 

• Adenomyosis: A condition where the endometrium grows into the muscle layers of the uterus.
• Bleeding disorders: von Willebrand disease (VWD) and platelet function disorders reduce the ability to clot effectively. 
• Cancer: This includes reproductive cancers like uterine and endometrial cancer.  
• Endometrial hyperplasia: An overgrowth of the uterine lining caused by high estrogen and low progesterone that can lead to endometrial cancer. 
• Fibroids: Leiomyomas or fibroids are a type of non-cancerous tumor that grow within the layer of the uterus.  
• Polycystic ovarian syndrome (PCOS): Long menstrual cycles and hormonal imbalances can thicken the uterine lining. 
• Polyps: Another type of non-cancerous uterine growth that can affect the endometrium.
• Thyroid disease: An underactive thyroid, or hypothyroidism, can delay ovulation and lead to a thicker uterine lining. 

It’s worth getting your symptoms evaluated if you have heavy periods and endometriosis, and not just assuming that the bleeding is related to your endometriosis. Endometriosis can co-occur with other conditions, so it’s important to let your healthcare provider know if you’re experiencing changes in your cycle. 

How do doctors evaluate heavy bleeding and clots?

Your healthcare provider may run multiple tests when assessing your heavy uterine bleeding. These tests typically include blood tests and imaging. 

Blood tests

These can check your hormone levels and the balance of estrogen and progesterone. They may also run a complete blood count (CBC) and check your iron levels to see if you have anemia.Your may also have bloodwork to rule out other conditions like hypothyroidism and bleeding disorders. 

Imaging

Your healthcare provider may perform an ultrasound to check for fibroids or other blockages or masses within the uterus. They may also order an ultrasound to see if they can detect endometriosis lesions, though endometriosis doesn’t always appear on imaging. 

It’s important to keep a log of your periods, especially if you’re experiencing heavy bleeding. Keep a record to share with your healthcare provider of how frequently you’re changing your pad or tampon and the number of clots you’re passing. 

How are endometriosis clots and heavy bleeding treated?

The treatment for clots and heavy bleeding will likely depend on your endometriosis management plan. If you’re not trying to conceive, your healthcare provider may recommend hormone-based medications or an IUD to regulate your hormones and limit the growth of your uterine lining. 

If you are trying to conceive, or do not do well on hormonal therapies, your healthcare provider may recommend endometriosis surgery to remove lesions, which can help reduce inflammation and lessen menstrual pain and bleeding. 

Your healthcare provider may also prescribe medications to help manage the bleeding during heavy periods. These medications may include tranexamic acid and nonsteroidal antinflammatories (NSAIDs). 

If you have tried medications and surgery and are experiencing consistent or severe pelvic pain, your healthcare provider may recommend a hysterectomy, a procedure that removes your uterus. Hysterectomies are usually the last resort when endometriosis symptoms  limit everyday life and fail to respond to other treatments. Hysterectomies are not first-line treatments for heavy uterine bleeding. 

The bottom line

Heavy bleeding and period clots are a fairly common experience among people with endometriosis. But that doesn’t mean you don’t have options for treating your symptoms. Managing your endometriosis through medication or surgery can help balance hormones and reduce inflammation, which, in turn, can help lessen bleeding and clots. 

Key takeaways

• Menstrual blood clots are normal. Small clots are common, especially on heavy flow days or after periods of rest. 
• Clots may be different if you have endometriosis. People with endometriosis may experience larger and more frequent clots.
• Just because clots are common, doesn’t mean you should ignore them. Talk to your healthcare provider if you notice frequent, large clots, especially those bigger than a quarter, along with heavy bleeding.
• Know the signs of dangerous blood loss. These include periods lasting more than seven days, changing your pad or tampon every two hours or less, and symptoms like lightheadedness and fatigue. 

Frequently asked questions (FAQs)

Is it normal to pass blood clots with endometriosis? Small, infrequent blood clots are a normal part of menstruation. But, if you have endometriosis, you may experience more frequent and larger clots. 

What are severe signs of endometriosis? Severe signs of endometriosis include chronic pain that makes it difficult to work or go to school, infertility, fatigue, frequent bloating, and pain during urination, bowel movements, and intimacy. 

What does a flare-up of endometriosis feel like? Endometriosis pain can happen at any time but tends to be the worst during your period. Pain can include severe cramping, heavy bleeding, sharp pelvic pain, bloating, and fatigue. 

‍What do endometriosis blood clots look like? Endometriosis blood clots tend to look like other menstrual blood clots, but may be larger and more frequent. Period blood clots may appear stringy or round and jelly-like. They can range in color too, from bright red to a reddish-brown, depending on how long the blood has been sitting for.