Period Blood Clots: Cause for Concern?

While usually normal, some may be a sign of an underlying medical condition

Occasional blood clots during your period are generally nothing to worry about; these can develop when the lining of the uterus (womb) is shed during your normal menstrual cycle. But when a clot is the size of a quarter or larger and/or is accompanied by extreme pain or a heavy flow, it may be due to a more serious condition like endometriosis, polycystic ovary syndrome (PCOS), or even cancer.

This article explains why period blood clots occur, as well as the signs and symptoms of abnormal clotting that need to be seen by a healthcare provider.

What Causes Normal Period Blood Clots?

Your period starts when hormones trigger your body to shed the lining of the uterus, known as the endometrium. As the lining detaches, small blood vessels called capillaries will rupture and bleed, causing your monthly flow.

To prevent too much blood from being lost, your body will respond by forming blood clots. It does so with blood cells called platelets that clump together to plug the ruptured vessels. Proteins called clotting factors help stabilize and strengthen the clot by producing a tough fibrous compound known as fibrin.

In order to pass larger clots, the cervix has to dilate, causing pain that can sometimes be intense. This partially explains why, if you have a heavy flow, you're more likely to have cramping.

What Does a Normal Period Blood Clot Look Like?

A period blood clot looks like a dark red blob of blood. The clots can vary in size, but a normal blood clot is about the size of a dime.

Mixed with menstrual blood may be bits of tissue from the uterine lining. Thus, what appears to be a blood clot may actually be a clump of shed tissues or a mixture of clots and tissues. These jelly-like globs are normal and usually nothing to be concerned about. 

When your menstrual flow is heavy, blood clots tend to be larger because there's a larger amount of blood sitting in the uterus. The blood may also be thick or stringy.

The color of period blood clots can also vary. Your period may start with bright red clots due to the rapid release of blood from the uterus. When the flow is at its heaviest, the clots may be dark red or even blackish, only to lighten up again as your period starts to end.

Abnormal Period Blood Clots

There are times when a period clot is a cause for concern. This is usually when a clot is excessively large due to abnormal menstrual bleeding, known as menorrhagia. Menorrhagia refers to heavy bleeding that lasts more than seven days.

How Heavy Is Heavy?

Your flow is considered heavy when you have to change your sanitary pad or tampon after less than two hours or you are passing clots that are the size of a quarter or larger.

Depending on your age and medical history, there are many conditions associated with menorrhagia, including:

  • Uterine fibroids: These common, benign (noncancerous) growths in the uterus often cause heavy bleeding.
  • Menopause: Changes in hormones during menopause can cause irregular and sometimes heavy bleeding.
  • Thyroid disease: Both hypothyroidism (overactive thyroid) and hyperthyroidism (underactive thyroid) can upset the balance of hormones and trigger heavy bleeding
  • Polycystic ovary syndrome (PCOS): Heavy bleeding is characteristic of this hormonal disorder that causes fluid-filled cysts in or on the ovaries.
  • Endometriosis: This is a condition in which endometrial tissue grows outside the uterus, causing adhesions (stuck-together tissues), pain, and abnormal bleeding.
  • Adenomyosis: This is a condition where endometrial tissue grows into the uterine wall, making it vulnerable to heavy bleeding whenever the lining is shed.
  • Miscarriage: This can happen very early in a pregnancy, sometimes before you even know you're pregnant. Clotting and bleeding are common.
  • Ectopic pregnancy: This is a potentially life-threatening situation in which a fetus has implanted outside of the uterus, often in a fallopian tube.
  • Uterine cancer or cervical cancer: These are potential but less likely causes of abnormal menstrual bleeding and blood clots.

When to See a Healthcare Provider

When to See a Doctor for Blood Clots

Verywell / Emily Roberts

See your healthcare provider immediately if you experience any of the following:

  • Blood clots are larger than a quarter.
  • There is an excessive amount of clots.
  • Menstrual bleeding is heavy and requires you to change your tampon or pad every couple of hours.
  • Bleeding lasts longer than seven days.
  • You have extreme abdominal pain with nausea or vomiting.

How to Respond to Clots During Pregnancy

If you're pregnant and passing blood or clots of any kind, see your healthcare provider or go to the nearest emergency room. Heavy bleeding with clots and painful cramping may be signs of miscarriage. 

Diagnosing the Cause of Abnormal Period Clot

If you see a healthcare provider about period blood clots, they will start by asking questions that can help direct the diagnosis, such as:

  • How long does your period last?
  • How heavy is your usual flow?
  • Have you noticed changes in your flow over time?
  • What size are the clots?
  • Have you been pregnant before?
  • Have you ever had pelvic surgery?
  • Do you use birth control and, if so, what kind?
  • What medications are you on?

They will also likely perform a pelvic exam and order a battery of tests to figure out what might be causing your blood clots.

Lab Tests and Procedure

The following lab tests and procedures may be ordered to indirectly or directly check for problems with your uterus or conditions affecting the uterus:

  • Blood tests: Various blood tests can check for thyroid problems, hormonal imbalances, anemia, or a problem with your platelets.
  • Pap test: This is a procedure in which a swab removes cells from the surface of the cervix to examine under the microscope.
  • Ultrasound: This non-invasive imaging procedure uses sound waves to evaluate uterine blood flow and detect problems like fibroids or endometriosis.
  • Hysteroscopy: This involves the insertion of a lighted scope through the cervix to view inside the uterus.
  • Endometrial biopsy: This involves the removal of a sample of endometrial tissue to view under a microscope.
  • Sonohysterogram: This is a specialized ultrasound in which saline fluid is injected into the uterus so that the expanded organ is easier to view.
  • Computerized tomography (CT): The imaging test composites multiple X-rays that can create three-dimensional "slices" of the uterus.
  • Magnetic resonance imaging (MRI): This imaging technology uses powerful magnetic and radio waves to create highly detailed images of soft tissues.

Blood Clots Healthcare Provider Discussion Guide

Get our printable guide for your next healthcare provider's appointment to help you ask the right questions.

Doctor Discussion Guide Woman

Treatment of Abnormal Period Blood Clots

The treatment of abnormal period blood clots may include iron supplements, hormone therapy, medications, and—in some cases—surgery. The treatment plan will vary based on the cause and severity of your symptoms as well as your age and plans for pregnancy.

Iron Supplements

Prolonged, heavy menstrual bleeding is a common cause of anemia. One study found that 63.4% of people with menorrhagia also had anemia.

To treat anemia, your healthcare provider may prescribe iron supplements. Iron is the main component of hemoglobin, a protein on red blood cells that carries oxygen to cells, and, without enough of it, you can have iron-deficiency anemia.

Iron supplements will not make your period lighter, but they can help overcome fatigue and tiredness associated with menorrhagia.

Hormonal Contraceptives

Certain hormonal contraceptives may help control irregular bleeding by altering the menstrual cycle:


Advil or Motrin (ibuprofen) are non-steroidal anti-inflammatory drugs (NSAIDs) that not only treat pain but also reduce inflammation. Studies have shown that these anti-inflammatory effects can reduce heavy menstrual by up to 49%.

Other NSAIDs like aspirin or Aleve (naproxen) do not have these effects and can actually increase menstrual bleeding.

Hormonal Therapy

Progesterone, estrogen, or a combination of the two can help reduce bleeding. These can be found in contraceptives, but healthcare practitioners can also prescribe hormones in doses that are not tailored for birth control. This is referred to as therapeutic hormonal therapy (THT).

Hormonal Therapy or Birth Control?

The main advantage of therapeutic hormone therapy over hormonal birth control is that you can still conceive while on treatment.

Antifibrinolytic Medicine

Antifibrinolytic medicines like Lysteda (tranexamic acid) or Amicar (aminocaproic acid) can help reduce heavy menstrual bleeding. They do so by preventing the breakdown of fibrin produced by clotting factors in the blood. By slowing the breakdown of clots, bleeding can be reduced.

Studies have shown that Lysteda can reduce heavy menstrual flow by up to 58%.


Surgery may be an option if you have polyps or fibroids. Your healthcare provider may also recommend surgery if conservative treatments for menorrhagia fail to provide relief.

Surgical options include:

  • Laparoscopy: This minimally invasive surgery can remove small uterine fibroids with two or more small incisions in your abdomen.
  • Myomectomy: This is an operation to remove fibroids while preserving the uterus.
  • Endometrial ablation: This a procedure that destroys (ablate) all or part of the uterine lining to reduce or stop periods.
  • Hysterectomy: This is the surgical removal of the uterus.

Pregnancy Considerations

You will no longer be able to get pregnant after undergoing a hysterectomy and will be less likely to do so after endometrial ablation. Speak with your healthcare provider about fertility-preserving treatments if you are trying or intend to get pregnant.


In general, period blood clots aren't something to worry about. But if you have heavy menstrual bleeding, numerous clots, severe menstrual pain, and clots the size of a quarter or larger, it is important to see a healthcare provider for a diagnosis and treatment.

Treatment may include oral painkillers, iron supplements, hormonal contraceptives, hormone replacement therapy, antifibrinolytic drugs, or uterine surgery.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Tracee Cornforth
Tracee Cornforth is a freelance writer who covers menstruation, menstrual disorders, and other women's health issues.