What Are the Common Causes of a Heavy Period with Clotting?

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  • Written By: Rebecca Harkin
  • Edited By: Allegra J. Lingo
  • Last Modified Date: 03 March 2020
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The most common causes of a heavy period with clotting are hormonal changes, fibroid tumors, a miscarriage, an abnormally large uterus, and some medications. One or two abnormal menstrual cycles are not cause for concern. If heavy menstruation with clotting occurs for several months, is accompanied by fatigue, a pale complexion, or dizziness, a gynecologist should be consulted to evaluate the cause and treat the problem.

Hormonal changes are one of the most common causes of a heavy period and clotting. Normally, the hormones progesterone and estrogen work together to control the menstrual cycle. If the levels of these hormones change, the result can be a heavy period with clotting. Some of the reasons hormones can get out of balance are the onset of menopause, weight gain or loss, and some medications.

Fibroid tumors and endometrial hyperplasia are two other common causes of a heavier than normal period with clotting. A fibroid tumor is a benign growth found in the uterus. These growths may cause excess menstrual bleeding and clotting by physically interfering with the normal clotting of uterine blood vessels or the growing fibroid tumors may influence the growth and size of blood vessels in the uterus, causing more uterine blood. Endometrial hyperplasia is the formation of a dense, thick lining of endometrial cells in the uterus and is typically caused by an excess of estrogen. A thicker lining can lead to heavier bleeding and clots.


A miscarriage is another cause of a heavy period with clotting. When a miscarriage occurs, the bleeding can range from light to heavy depending on the stage of pregnancy and the cause of the miscarriage. Clotting is usually the result of the normal shedding of the built up uterine lining and from fetal tissue. A miscarriage is often accompanied by cramping. When bleeding and cramping are severe, a doctor should be seen.

During pregnancy, the uterus becomes enlarged, stretched out by the growing baby. Soon after birth, the uterus normally contracts to its pre-pregnancy size, but in some cases the uterus can remain enlarged. When this occurs, heavy periods with clotting can occur due to the shedding of the excessive surface area in the enlarged uterus. An expanded uterus can also trap blood, forming large clots which are eventually expelled.

Some medications which can act as a blood thinner, such as aspirin, and blood thinners can produce heavy bleeding with clotting. During menstruation, the uterine blood vessels are exposed as the endometrial lining falls away, causing blood to be released. Towards the end of menstruation, the blood vessels gradually close. Aspirin and blood thinners can interfere with the constriction of the blood vessels, causing heavier and longer menstrual flow.


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Post 2

I had a heavy period once and had clots. One morning, I started having hideous, sudden cramps and I could tell *something* was happening. I ran to the bathroom, feeling like I was bleeding to death, and passed what I thought was a ginormous clot. Only it was pink looking and thick. Scared me to death.

I would have probably been a little more rational had it not been accompanied by more blood than I'd ever had before -- or since. My doctor said it was a "decidual cast" and happened occasionally. She said the bleeding was normal since it was apparently half my uterine lining all coming out at one time. I was in the bathtub rinsing it all off

, and it looked like the shower scene in "Psycho" -- no lie. It looked like at least a quart of blood, but I know it wasn't that much, of course. Still, it was plenty scary.

So it's not just miscarriages that cause heavy clots.

Post 1

Until I got on the pill, I had heavy periods with clotting every month. Lord, some of the clots I'd have were the size of quarters! I'd go eight days, with about four days of heavy flow, and the cramps were unreal, along with vicious backaches, tender breasts, awful mood swings -- you name it.

Since the pill helped me so much, it stands to reason that my hormones must have been wildly out of whack, and the pill helped regulate them to something approaching normal levels. Suffice it to say, the pill absolutely changed my life! I've been a different person since I've been on it.

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