Sep 2021

Blood Clotting During Your Period

  • By: Samantha Denäe

Blood clots during your period is something we all experience but have you ever wondered why they form? And why you may have so many? 

Although clots are normal and a natural defense mechanism for the body, blood clots are a mixture of blood cells, uterine lining tissue, and proteins in the blood which are used to aid in regulating its flow. As your body is preventing losing too much blood, it will form blood clots through a combo of plasma (liquid portion of blood) and platelets (blood cells that bind to form clots). As your lining sheds during the period, small blood vessels will bleed. Clots can also be mistaken for clumps of endometrial tissue.

During the period, endometrial cells lining the uterus strips away and leave the body. While this happens, proteins that causes blood in the uterus will release and coagulate, preventing blood vessels from continuing to bleed. Previously shedded blood also contain these coagulation proteins.

When the period is of a heavier flow, there is most likely a large amount of blood within the uterus, so when passing a blood clot, the cervix is dilating a bit which causes intense pain (cramps), and causes the coagulated proteins within the blood to clump (clotting). 

Blood clots dark red or blackish in color can appear during the heaviest part of your period. 

Contact your physician if the clots:

  • are quarter seized or larger
  • frequent
  • occurs with an abnormal heavy flow, requiring the change of a pad or tampon at least every 1–2 hours
  • occurs with significant pain

Frequent blood clotting during the period can be a sign of a deeper health issue like:

  • Menorrhagia: heavy menstrual bleeding lasting more than 7 days causing you to change your pad or tampon after less than two hours, or passing quarter-sized or larger blood clots.
  • Uterine Fibroids: noncancerous uterus growths. 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.
  • Endometriosis: where the endometrial like tissue in the uterine lining grows outside of the uterus, usually onto your fallopian tubes and ovaries, but can grow anywhere else in the body.
  • Adenomyosis: where the endometrial tissue in your uterine lining grows into your uterine wall, resulting in often enlarging the uterus.
  • Hormonal imbalances: PCOS, Hypothyroidism, perimenopause (the transition into menopause) and menopause can cause an irregular shedding of the uterine lining, which can result in clotting and heavy bleeding.
  • Miscarriage: Clotting and bleeding are common symptoms of a miscarriage.
  • Cesarian scar: can cause abnormal bleeding and clotting.
  • Cancer in your uterus or cervix: typically less likely but blood clots can be an indication of cancer.

If you think there may be an underlying issue from blood clotting you could ask for the following from your doctor:

  • Blood tests: check your thyroid function, hormone levels, anemia, or an issue with how your blood clots.
  • Pap test: Cells taken from the cervix can be examined to see if any changes might be the cause of heavy bleeding and/or clots.
  • Ultrasound: can monitor blood flow and check for problems like fibroids or an enlarged uterus.
  • Endometrial biopsy: samples of tissue from the uterine lining are taken and evaluated for abnormal cells.
  • Sonohysterogram: examining the uterine lining, fluid will be injected into the uterus through a tube that is inserted through the vagina and cervix.
  • Hysteroscopy: a thin scope is inserted into your uterus to examine in detail. A hysteroscopy can help to diagnose polyps and fibroids.
  • Computerized tomography (CT) or magnetic resonance imaging (MRI): MRIs will use powerful magnets and radio waves to generate a picture of the uterus. A CT is like an X-ray.


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