What are the Reasons for Passing Blood Clots During a Period?

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  • Written By: N. Ayers
  • Edited By: A. Joseph
  • Last Modified Date: 29 August 2018
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The passing of blood clots during a period is normal, because the thickened uterus lining is being shed and expelled. Other reasons for clotting during menstruation can include certain lifestyle changes, such as weight loss or medication. A visit to a medical professional might be necessary if the frequency of blood clots increases, because serious health problems could be developing.

A heavy flow is among the reasons for passing blood clots during a period. Anticoagulants that the body produces to allow the blood flow and prevent clots are not as effective during heavy menstrual cycles. As a result, clotting is more likely to occur and might cause the menstrual bleeding to seem thicker.

Miscarriage, the termination of a pregnancy, can also cause a woman to pass blood clots. In the case of a miscarriage where disorders such as lupus are evident, clotting prevents the placenta from receiving blood. Over-the-counter medications such as baby aspirin can be used to thin the blood and lower the risk of clots in these circumstances.

Fibroid tumors that grow in the uterus also contribute to the passing of blood clots during a period. These non-cancerous tumors are likely to cause heavy and abnormal menstrual bleeding. As a result, fibroids increase the amount of clots that form during menstruation.


A hormonal imbalance of progesterone and estrogen is another cause of clots during a period. The progesterone hormone is produced by the ovaries to help the uterus prepare for fertilization when an egg is released. Estrogen aids in the reproduction process, the development of female sexual characteristics and the regulation of a menstrual cycle. The balance between progesterone and estrogen can be disturbed because of a variety of factors, including menopause, medication, significant weight loss or gain, benign polyps, and endometriosis. When an imbalance occurs, the lining of the uterus becomes thick and causes heavier bleeding, which increases the development of blood clots.

Pelvic inflammatory disease (PID) might be one of the more serious reasons for passing blood clots during menstruation. This disease is an infection of the reproductive organs, including the fallopian tubes, uterus and cervix. PID causes abnormal menstrual bleeding and is associated with sexually transmitted diseases, including gonorrhea and chlamydia.

Birth control methods such as oral contraception, the use of an intrauterine device (IUD) and the use of an injected contraceptive can also cause a woman to pass blood clots during her period. The side effects of these birth control methods include heavier, irregular and prolonged menstrual bleeding, which increases the risk of clotting.


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Post 13

My last period was on June 8th and have been waiting to get my period. I took a HPT and it was positive with a slight faint line and a darker line on Saturday. Today I passed a large blood clot. Am I miscarrying? Have twinges in my stomach and breasts hurt.

Post 12

I am 19 and I have had my period for years, but after a while, they became so bad that I was leaving school to go home. I would throw up for days and I would cramp the entire period.

A few years ago, I started birth control. At first it helped out like a lot, but then after a while, it was like I wasn’t taking them. The bad cramps came back, my period became heavier, I threw up much more and i would be miserable for days. While they were bad, I noticed I would pass what looked a lot like raw liver, and the clots were the size of the palm of my hand. Is this normal and what should I do about this?

Post 11

My daughter gets her flow very unexpectedly, and she has major blood clots mainly. She has stained her clothes at school. Then one of my friend suggested we try the Adira period panty. I ordered them online for my daughter. She has never stained after starting to use them. I suggest them to everyone who has staining issues. They are cotton and very comfy.

Post 10

I started my period and it was spotting at first but the spotting was dark black, then later on in the day, I checked again and the blood was still super dark, but this time. it was super thick as well. What could this possibly mean? I recently took a plan B pill a couple of weeks before and I'm on birth control.

Post 9

It's the third day of my period and I started passing egg size clots. It came suddenly, without any cramping or any pain. My bleeding is usually on the heavier side on the second and third day and the clots are usually size of a pea. Those look like chopped liver, and are bright to dark red. I had a bad migraine yesterday and today so I took a dose of Excedrin (which contains aspirin). Is it possible aspirin could cause those huge clots?

Post 8

I think hormonal changes have a lot to do with blood clots. It's a good idea to check estrogen and progesterone levels if sudden changes take place with periods. Thyroid hormones might affect it too.

I recently started getting my periods in two days (usually it's four) with a lot of blood clots. It turned out that my thyroid hormone levels were abnormal.

Post 7

@RoseKitten-- Hey, was this during your period?

If so, it sounds normal although I've never seen a white blood clot before. If this happened when you were not having your period, you need to see your doctor!

Post 6

Actually, a blood clot during period and the passing of uterus lining is not the same thing. Blood clots usually have a different look to them and will be a bright red color. Whereas the uterus lining that is being shed during a period will be a different color. Sometimes it is pinkish, sometimes it is a dark red color, but never a bright red. It can also be in different shapes, but it will have the texture of thick tissue, much like the texture of chicken liver.

Many women confuse the two with one another. The whole purpose of a period is to get rid of the uterus lining so that a new one can be made by the body for the following month. This is the body's preparation for conception. So of course, it's absolutely normal.

Post 5

I had a blood clot the size of my palm. It was dark red and white. Any idea what caused this? I had severe cramps just before.

Post 3

@alisha-- I think it also depends on how large the blood clots are. I used to get big blood clots during my period while I was on oral contraceptives. I told my doctor about it and he said it's fine, unless the clots are extremely large. If it's ever the size of a chicken liver, there might be something more serious going on. I've never had any that size.

I also remember my doctor telling me that clotting tends to happen towards the end of the period because the old blood that has been waiting clots and also becomes a darker color (not bright red). So it might be unusual to have very large blood clots, and / or to have them very early in the period.

Post 2

@alisha-- That's a good question. I've asked my mom the same. I'm lucky because my mom is a nurse and I can ask her anything.

She told me that blood clotting during periods is normal. The dark pink clots you're seeing aren't actually blood clots. Those are parts of the endometrium that gets thrown out with the period. Every month, our body builds a new endometrium.

Blood clots are the dark red chunks and those are mostly normal too, according to my mom. She says that blood tends to clot while it is flowing out from the uterus. Unless you're taking medications or have other symptoms, I don't think you need to be worried. But don't be scared to ask your doctor about it. We have to confide in our doctors so that they can treat us if there is something wrong.

Post 1

I always get heavy clotting during my period. But what do period clots look like exactly?

Because the clots I get don't always look the same. Sometimes it's a really dark red and smaller and sometimes it's a dark pink and larger. Are those both blood clots?

Do you think this is normal? I've always thought that it's normal because that's how my periods have always been. I'm too shy to ask my doctor about it.

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