Why do blood clots occur during menstruation?

By (embryologist), (gynecologist), (embryologist) and (psychologist).
Last Update: 02/08/2022

Many women have clots in their menstrual bleeding and this can be considered normal. Generally, these clots are due to heavy bleeding, are usually not large, and do not cause pain.

However, there are certain situations in which clots in the period may indicate underlying pathology, so it will be advisable to consult a specialist so that he/she can assess the causes of menstrual clots.

What are menstrual clots?

Menstruation is the beginning of a woman's menstrual cycle. This is the shedding and expulsion of the endometrium, which is the mucous membrane that lines the uterus, as a result of the failure of the previous menstrual cycle to produce a pregnancy.

The endometrium will grow again to be in the best conditions for the next cycle since it is the layer where the embryo must implant.

Although this menstrual bleeding usually flows smoothly, some women notice small clots or "lumps" in their menses. The consistency of these clots can be gelatinous or thick and their size usually does not exceed that of a coin.

As for the color, the clot may be deep red or a stronger red than the rest of the menstrual bleeding. In addition, this color may vary depending on the day of menstruation, since at the end of the period the clots will tend to have a darker color, almost brown.

In general, the expulsion of these clots in the period is completely normal in many women and should not be a cause for concern.

However, menstrual clots are a reason to consult a specialist if they are frequent, large, or occur with other symptoms. The reason is that, in these cases, the presence of clots may be related to some pathologies.

Why are there clots in the period?

Menstrual clots usually occur when menstrual bleeding is very heavy. In fact, it is more common for women to observe these clots in the first days of menstruation when bleeding is usually more intense.

However, the presence of clots in the period may be a one-time occurrence. The amount of menstrual bleeding is different in each cycle for the same woman. Thus, it is possible that there may be clots only at a certain period or because of a temporary hormonal imbalance.

When can they indicate pathology?

A woman should see a specialist if she has clots of considerable size or very frequent clots in her menstruation. Likewise, the woman should also go for consultation if the clots occur together with symptoms such as the following:

  • Heavy bleeding, which requires changing the menstrual pad, tampon or menstrual cup every few days.
  • Menstrual pain.
  • Tiredness and fatigue.

In this case, it may be useful for the woman to write down the characteristics of her menstruation (duration, time at which she renews the pad, tampon, or menstrual cup...) and of the clots (texture, size, color, days of appearance, if it is the first cycle that they are expelled...), as well as all the symptoms she has experienced.

Possible pathologies

There are different situations that can lead to the appearance of menstrual clots. Among them, we can mention the following:

  • Hormonal imbalance: altered levels of sex hormones can cause the appearance of clots in menstrual blood.
  • Fibroids or polyps: Uterine growths in the form of fibroids or polyps may be accompanied by heavy menstrual periods and the expulsion of clots.
  • Endometriosis: this is a pathology in which endometrial tissue grows outside the uterine cavity. A woman with endometriosis has very painful menstrual periods, which may also be heavy.
  • Adenomyosis: is the presence of endometrial tissue in the muscular layer of the uterus and can also cause heavy menstruation with clots.
  • Blood problems: Certain blood conditions such as von Willebrand' s disease can cause very heavy menstrual bleeding.

However, the frequent occurrence of clots and heavy periods may also be caused by the woman having an enlarged uterus or by iron deficiency anemia.

On the other hand, if the woman is seeking pregnancy, heavy bleeding and the appearance of large yellow or grayish clots could indicate a miscarriage.


When a patient sees a gynecologist for the presence of clots in menstruation, the gynecologist will ask about her medical history and may perform different tests depending on her symptoms.

In general, the woman will undergo an ultrasound to evaluate the uterine cavity in search of any alteration such as fibroids. In addition, the patient will be asked to have a blood test to see if she is anemic, for example.

Thus, the specialist will be able to investigate the causes of menstrual clots, in order to be able to indicate to the woman the appropriate treatment if necessary, which will depend on the situation and the reproductive desires of the patient.

FAQs from users

Can clots in menstruation indicate infertility?

By Júlia Roig Navarro M.D. (gynecologist).

It does not have to be. If a cause that may also affect fertility is ruled out, it is possible to have abundant periods, with clots, without these indicating a problem. However, you should check that it does not lead to anemia and, if it does, treat it.
Read more

Is it normal to have clots during menstruation?

By Andrea Rodrigo B.Sc., M.Sc. (embryologist).

Yes, most women have had clots in their menstrual bleeding at least once and usually on several occasions. The size as well as the color varies between women and between periods of the same woman depending mainly on the cause.

Could clots in the period bleeding be the cause of period pain?

By Andrea Rodrigo B.Sc., M.Sc. (embryologist).

Clots themselves do not cause pain, but they usually appear when bleeding is heavy and dense and this can influence menstrual pain. Both pain and the appearance of clots can be symptoms of increased vaginal bleeding.

How can I reduce clots in menstruation?

By Andrea Rodrigo B.Sc., M.Sc. (embryologist).

There is no clear way or method for the occurrence of clots in the period. However, it is advisable to lead a healthy lifestyle that allows for proper overall blood circulation. It is recommended to reduce stress and consume foods rich in bioflavonoids such as broccoli, grapes, citrus fruits, cherries, tomatoes, or green peppers to help strengthen blood vessels and reduce clotting.

On the other hand, if the appearance of clots is very common or is accompanied by pain, it is advisable to consult a doctor. Normally, in these cases, the specialist will prescribe some medication to help control vaginal bleeding such as birth control pills, aspirin, or mefenamic acid.

Could the myoma be the cause of the clots in the period?

By Andrea Rodrigo B.Sc., M.Sc. (embryologist).

Yes, fibroids and cysts can increase the occurrence of bleeding or cause alterations in bleeding that lead to clots. In any case, having a fibroid does not necessarily indicate that the vaginal bleeding has clots.

Does menstruation with or without clots favor pregnancy?

By Andrea Rodrigo B.Sc., M.Sc. (embryologist).

Clots usually do not affect conception. The fact that vaginal bleeding has clots does not indicate that pregnancy will be more or less easy to achieve. If clots are common and pregnancy does not occur, it is advisable to consult a specialist in case there is a problem with the receptivity of the endometrium.

Is it bad to have a period with brown or brown clots?

By Silvia Azaña Gutiérrez B.Sc., M.Sc. (embryologist).

It doesn't have to be. It is true that clots in menstruation may be more frequent in the first days of menstruation, when the bleeding is more abundant and, therefore, usually have a deep red or darker red color than the rest of the bleeding. Thus, dark brown or coffee-colored clots may appear at the end of the period, as the blood is "aged".

In general, clots in menstruation are normal and occur in many women. However, if these clots appear frequently, are large and/or are accompanied by symptoms such as heavy bleeding, pain or tiredness, it is best to consult a specialist, as they may be caused by an underlying pathology.

If you are interested in learning more about menstruation, we recommend you visit the following link: Menstruation: symptoms and characteristics of bleeding.

On the other hand, if you want to learn more about the menstrual cycle, you can read this article: The menstrual cycle: what happens in each of its phases?

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Borzutzky C, Jaffray J. Diagnosis and Management of Heavy Menstrual Bleeding and Bleeding Disorders in Adolescents. JAMA Pediatr. 2020 Feb 1;174(2):186-194. (See)

Bradley LD, Gueye NA. The medical management of abnormal uterine bleeding in reproductive-aged women. Am J Obstet Gynecol. 2016 Jan;214(1):31-44. (See)

Davies J, Kadir RA. Heavy menstrual bleeding: An update on management. Thromb Res. 2017 Mar;151 Suppl 1:S70-S77. (See)

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FAQs from users: 'Can clots in menstruation indicate infertility?', 'Is it normal to have clots during menstruation?', 'Could clots in the period bleeding be the cause of period pain?', 'How can I reduce clots in menstruation?', 'Could the myoma be the cause of the clots in the period?', 'Does menstruation with or without clots favor pregnancy?' and 'Is it bad to have a period with brown or brown clots?'.

Read more

Authors and contributors

 Andrea Rodrigo
Andrea Rodrigo
B.Sc., M.Sc.
Bachelor's Degree in Biotechnology from the Polytechnic University of Valencia. Master's Degree in Biotechnology of Human Assisted Reproduction from the University of Valencia along with the Valencian Infertility Institute (IVI). Postgraduate course in Medical Genetics. More information about Andrea Rodrigo
 Júlia Roig Navarro
Júlia Roig Navarro
Dr. Júlia Roig has a degree in Medicine and General Surgery from the University of Barcelona (UB). In addition, she is a specialist in Gynecology and Obstetrics at the Hospital Universitari Arnau de Vilanova and has a Master in Human Assisted Reproduction from the Complutense University of Madrid and did an internship at the Quirón Dexeus center in Barcelona. More information about Júlia Roig Navarro
Member number: 56030
 Silvia Azaña Gutiérrez
Silvia Azaña Gutiérrez
B.Sc., M.Sc.
Graduate in Health Biology from the University of Alcalá and specialized in Clinical Genetics from the same university. Master in Assisted Reproduction by the University of Valencia in collaboration with IVI clinics. More information about Silvia Azaña Gutiérrez
License: 3435-CV
Adapted into english by:
 Cristina  Algarra Goosman
Cristina Algarra Goosman
B.Sc., M.Sc.
Graduated in Psychology by the University of Valencia (UV) and specialized in Clinical Psychology by the European University Center and specific training in Infertility: Legal, Medical and Psychosocial Aspects by University of Valencia (UV) and ADEIT.
More information about Cristina Algarra Goosman
Member number: CV16874

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