Menstrual clots are a mixture of blood cells, tissue from the lining of the uterus, and proteins in the blood that help regulate its flow.
Some medical conditions can cause large blood clots, often alongside heavy menstrual bleeding or period pains. People should see a doctor if they are concerned about their menstrual clots.
Is it normal to have clots in menstrual blood?
Blood clots are a natural part of menstruation.
It might be surprising to see a thick glob of menstrual blood, but, in most cases, blood clots are a natural part of menstruation.
They are also an example of the body's natural defense mechanism. The thick, jelly-like texture of a menstrual clot helps prevent too much blood from escaping.
This clotting function is beneficial elsewhere in the body when there is an injury to the tissue, such as a cut or laceration.
Menstrual clots generally occur when the flow is heavy. As a result, they are more common during the first 2 days of menstruation, which is typically the heaviest part of a period.
Clots arise as a result of the uterine lining shedding increased amounts of blood. When the blood pools in the uterus or vagina, it begins to coagulate, much like it would on an open skin wound.
The consistency of menstrual blood varies both throughout the period and from one period to another. People may experience a heavy flow containing menstrual clots one month, and a lighter flow with no clots the next month. This variation is natural and changes may occur due to diet and lifestyle factors.
Menstrual clots can be bright in color, or a darker, deeper red. More sizeable clots may look black. Menstrual blood begins to appear darker and more brown toward the end of each period as the blood is older and leaving the body less quickly.
Causes of menstrual clots
During menstruation, the endometrial cells that line the uterus strip away and leave the body. As this happens, the body releases proteins that cause the blood in the uterus to coagulate. This coagulation prevents the blood vessels in the uterine lining from continuing to bleed.
The blood that the body has already shed also contains these coagulation proteins.
When the flow is most substantial, the coagulation proteins within the blood may start to clump together, resulting in menstrual clots. This generally occurs when menstrual blood pools in the uterus or vagina before leaving the body.
Although it is normal to have clots in the blood during menstruation, this symptom can sometimes signal a medical issue. It is advisable to seek medical advice if the clots:
- are larger than a quarter in size
- are very frequent
- occur with an abnormally heavy flow that requires a person to change their pad or tampon at least every 1–2 hours
- occur with significant pain
The following conditions may cause abnormal menstrual clots:
Uterine polyps or fibroids
A blockage in the uterus may stop it from contracting as it should, meaning that it cannot force the blood out as quickly as usual. The blood will leave the body more slowly so it will have more time to pool and form clumps.
The blockage can also cause a heavier flow, which results in more blood pooling.
Blockages may occur as a result of growths in the uterus. These include uterine polyps and fibroids, which are not cancerous but can cause other health issues without proper management.
Uterine polyps and fibroids consist of either endometrial or muscular tissue that grows in the uterine wall. They can cause symptoms such as:
- persistent lower back pain
- pain during sex, or dyspareunia
- feeling bloated
- fertility issues
- irregular spotting
Endometriosis can cause painful and heavy periods.
Endometriosis is a condition that causes the tissues of the uterine lining to grow outside of the uterus. This abnormality can lead to several symptoms, which may be worse around the time of menstruation.
Symptoms of endometriosis often include:
- pain and cramping in the pelvis or lower back
- very heavy periods, or menorrhagia
- painful periods, or dysmenorrhea
- discomfort or pain during sex
- fertility issues
In people with adenomyosis, the uterine lining grows into the muscular wall of the uterus. This can make the endometrial lining and uterine wall much thicker, which can lead to a much heavier flow during a period. As a result, it is more likely that blood clots will appear in the menstrual blood.
The balance of hormones in the body is essential for maintaining a healthy uterus. If the levels of specific hormones become unbalanced, many issues can occur, including heavy menstruation or clotting.
During a miscarriage, or pregnancy loss, a person will usually pass a number of large clots, depending on the stage of the pregnancy. Pregnancy loss can sometimes occur before a person knows that they are pregnant so they may mistake an early miscarriage for a regular menstrual cycle.
After numerous pregnancies, a person's uterus will remain somewhat larger than it was before. An enlarged uterus can also be due to structural issues, such as fibroids. There will be additional space for the blood to pool in, which could lead to further clotting before it exits the body.
Some bleeding disorders may be responsible for heavy menstrual flow, as they can affect the coagulation proteins that the uterine lining needs to stop menstrual bleeding.
Disorders such as platelet function disorder or von Willebrand's disease (VWD) may cause abnormally heavy menstruation.
When to see a doctor
People who are experiencing very heavy menstrual bleeding or have clots larger than a quarter in their menstrual blood should see a doctor.
A person with heavy menstruation may have to change their pad, tampon, or menstrual cup more than once every 2 hours for part of their period. They may also need two pads at a time and may miss out on everyday activities due to their menstrual flow.
People with very heavy periods have a higher risk of iron-deficiency anemia. Anemia occurs when there are fewer red blood cells in the body than usual. Low iron levels can cause this because the body needs iron to make new healthy blood cells.
Other symptoms of iron deficiency include:
- general fatigue
- shortness of breath
Anyone who is uncertain about their menstrual clots should see a doctor.
Diagnosis and treatment
A diet that includes iron-rich foods may help with menstrual blood clots.
To diagnose the cause of abnormal menstrual clots, a doctor may ask about signs and symptoms, order blood or imaging tests, or carry out a physical examination.
Finding out the cause will allow a doctor to recommend the most appropriate course of treatment.
Doctors may advise taking an iron supplement if they believe that someone is losing too much blood or may be at risk of anemia. They may also suggest some actions that people can take at home, such as:
- staying hydrated with water
- avoiding aspirin, which may make bleeding worse
- eating a healthful diet that includes iron-rich foods
- doing regular physical activity
Doctors may prescribe hormonal medications to help balance the hormones and control heavy bleeding. Intrauterine devices (IUDs) containing progestin may reduce blood flow, and some birth control pills may also help.
Doctors may recommend taking nonsteroidal anti-inflammatory drugs (NSAIDs) during the period to help reduce symptoms, such as cramping, pain, and discomfort. The NSAIDs may also help with excessive bleeding.
People who prefer not to use hormone treatments may wish to try medications that control blood clotting instead.
Menstrual clots are normal and usually a symptom of heavy menstrual flow. However, anyone who notices a pattern of heavy flow or heavy clotting alongside other symptoms should see a doctor.
There are a few different causes of abnormal menstruation. A doctor can help find effective ways to treat the underlying issues and control frequent or large menstrual clots.