Blood Clots During a Period:
What's Normal, What's Not?

Blood Clots During a Period: What's Normal, What's Not?


What are period clots or menstrual clots?

Menstrual clots are lumps of coagulated blood or tissue. They are discharged from the uterus during menstruation when the lining of the uterus or endometrium sheds and is expelled from the uterus through the cervix.

Normally, the body produces substances known as anticoagulants [1], or blood thinners to allow the thickened endometrium fragments and blood mixture to pass more freely through the cervix and be expelled. However, sometimes, the body is not able to produce enough thinning agents, and this causes blood clots to form.

menstrual clots, period clot, Menstrual clots and endometriosis What does a menstrual clot look like?

Menstrual clots look like pieces of mashed up red fruit. They can be bright red or burgundy and may vary in size. They are usually mixed with liquid blood. The longer the blood stays inside the uterus, the darker it is in color, and the likelier it is to form clots.


Blood clot formation is the body’s way of controlling bleeding [2]. Blood cells called platelets play an important role in blood clot formation. They release chemicals that start the so-called “clotting cascade.” A protein called fibrin is the last step in this cascade, which crosslinks and forms a mesh-like structure that results in a clot [3].

Platelets may be triggered to produce these clotting factors. It happens in menstruation, whenever there is the pooling of blood as with heavy menstruation, and also as a result of an injury to a blood vessel wall, like for example in the case of a grazed knee.

Menstrual clots and heavy bleeding

The normal menstrual cycle lasts 25 to 32 days. A normal flow lasts between four and seven days and may be accompanied with blood clots. A normal period should normally cause mild to moderate discomfort starting from the first day and then subside.

A period is considered heavy if it soaks through a pad or tampon every hour for several hours or if it lasts for more than seven days [4]. Large clots in period blood are also considered to be a sign of heavy periods. Heavy periods can cause constant pain in the lower abdomen.

Heavy menstrual bleeding can negatively affect a woman's quality of life and lead to other conditions such as anemia [5]  in which there are not enough healthy red blood cells that can carry oxygen to different organs and tissues in the body. Anemia can make a person feel weak and tired.


Blood clots during a period can be normal or a sign of an underlying problem [4] such as:

  • A blockage in the uterus
  • Fibroids or non-cancerous growths in the wall of the uterus
  • Hormonal imbalance
  • A miscarriage

Menstrual blood clots can also indicate the presence of more serious conditions such as:

  • Endometriosis, a condition where the lining of the uterus or endometrium grows outside the uterus
  • Adenomyosis, a condition where the lining of the uterus or the endometrium grows into the wall of the uterus
  • Cancer

When should I worry?

Clots in menstrual blood are considered normal if they are quarter-sized or smaller and only occur occasionally. However, if they frequently occur (more then three times in a row) accompanied by heavy periods and are larger than a quarter, medical advice should be sought.

Menstrual clots and endometriosis

Endometriosis is usually accompanied by heavy bleeding during a woman’s period and chronic pelvic pain. This is because the endometrium that has grown outside the uterus reacts to the hormones secreted from the ovaries in the same way as the normal endometrium and starts to bleed too.


Hormonal medications such as the contraceptive pill can help regulate heavy bleeding and reduce the formation of blood clots [7]. These work by inhibiting the growth of the endometrium. An intrauterine device (IUD) that releases the hormone progestin and that is sometimes used as a method of contraception can also help.

Other treatment options include Cyklokapron [8] and Lysteda [9]. These medicines stop blood clots from breaking down and therefore may reduce heavy menstruation. This way it is hoped that less blood will be pooled in the uterus and menstrual clot formation will be reduced.

Laparoscopic surgery [10] that is often used both to diagnose and treat endometriosis can also be used to treat heavy bleeding and the formation of blood clots in periods.


“Endometriosis is associated with heavy periods, prolonged menstrual flow, and large clots. A transvaginal sonogram, and, if needed hysteroscopy and endometrial biopsy are necessary for diagnosis. Myoma, uterine fibroid, polyp, endometrial hyperplasia, and endometrial cancer must be the different diagnoses to be ruled out.” — Dr. Seckin, gynecologist, laparoscopic surgeon, and endometriosis expert.


My research led me to locate an excision specialist, Dr. Seckin. I had excision surgery with Dr. Seckin in March of 2015. I had advanced endometriosis removed in 18 places, including my appendix, intestines, ovary, and uterus. It turns out that the cyst was the least of my problems! Dr. Seckin was wonderful throughout my experience. Read More

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  • Grace Larsen

    After years of excessively painful periods, a serious loss of quality of life, and a series of uninformed and uninterested doctors, Dr. Seckin and Dr. Goldstein turned my life around. I was told I woke up from my surgery almost a year ago with a smile on my face, and I haven't stopped since. Before I heard of Dr. Seckin,…

  • Nicole Novakowski

  • Jacqueline Galindo

    Dr Seckin and his team gave me back my life! Tomorrow will be 1 month since my surgery and I feel great. Dr. Seckin, Dr Liu, and Dr Goldstein are not only beyond words talented and amazing Doctors, but they are also genuinely wonderful and caring people. I cannot say enough great things about Holly, Asiye and Kim as well.…

  • Anna Lu

    Dr. Seckin and his staff spared me from years and years of heavy periods and unbearable endometriosis pain. After having surgery with him (my first) I can now function like a regular human. No more eating NSAIDs like candy and calling out sick from work. Thank you, Dr. Seckin!

  • Sheena Wright

    I underwent surgery with Dr. Seckin in 2017 and have felt like a new woman ever since. If you have, or suspect you have endometriosis, Dr. Seckin and his compassionate team of surgeons and staff are a must-see.

  • Angela Aro

    I have struggled with endometriosis and adenomyosis since first starting my period at 13. I was diagnosed at 21 and what followed was a series of unsuccessful surgeries and treatments. My case was very aggressive and involved my urinary tract system and my intestines. After exhausting all of my local doctors I was lucky enough to find Dr. Seckin. We…

  • Emi O

    Seckin and Dr. Goldstein changed my life!

  • Kristin Sands

    Like so many women who have tirelessly sought a correct diagnosis and proper, thorough medical treatment for endometriosis, I found myself 26 years into this unwanted journey without clear answers or help from four previous gynecological doctors and two emergency laparoscopic surgeries. I desperately wanted to avoid the ER again; a CT scan for appendicitis also revealed a likely endometrioma…