Blood Clots During Your Period – What It Means

Humanity has had a mixed relationship with menstruation throughout the centuries. Some scholars have theorized that the monthly bleeding that women go through was the basis for the earliest religions we created. Depending on which faith you followed in the intervening years, you might have thought that a woman on her period was sacred (Ancient Rome), ritually unclean (Judaism and Islam) or just a woman on her period and nothing more or less (Buddhism and Sikhism).

With all the cultural taboos swirling around, not to mention the usual discomfort, having a period once a month can be a trial in itself. But when something happens differently than usual, it is natural to feel concerned.

Here is a look at the experience of forming blood clots during your period, what it means, and whether it is dangerous.

Why Do Clots Form?

First of all, you should know that blood clots are a normal and natural part of menstruation. Every 28 to 35 days, most women of childbearing age will shed the endometrium or the uterine lining. This layer grows throughout the month, as estrogen encourages it to thicken to prepare for the arrival of a fertilized egg.

If a fertilized egg doesn’t implant in the wall of the uterus, the body starts to absorb about two-thirds of the lining, and the other third begins to shed. As the lining is shedding, it becomes mixed with blood, mucus, and other tissue, and begins to pool at the bottom of the uterus, in preparation for the cervix contracting and expelling it into the vagina.

As it is pooling, the body produces anticoagulant hormones to thin the mixture. Sometimes, however, the blood flow is greater than the body’s capacity to produce these hormones, which causes clots to form. This is why clots are more common in the first days of a period, which is usually when the flow is heaviest.

How Do You Know If It’s Heavy Bleeding?

During the heaviest flow, blood clots may be dark red, brown, or black, as there has been more blood than your body has been able to thin. But most of the time, they will be a brighter red color.

As long as they’re not particularly large, there’s likely nothing to worry about. They may also appear darker again towards the end of your period, as the blood flow slows down and so the blood being expelled is older.

A normal flow should last for four or five days, and it should produce around two or three tablespoons’ worth of blood. The medical term for heavy menstrual bleeding is menorrhagia, which refers to bleeding that lasts for more than seven days, or which exceeds a total loss of 80ml (around five and a half teaspoons worth).

Of course, you can hardly be expected to stand there holding a spoon under yourself all day, so how can you tell if your bleeding is normal? Other than your own awareness of what is normal for you, there are a few signs that you can check for.

If any of the following are the case, then it’s a decent indication that you are experiencing a heavy period:

  • Bleeding through your clothes or bedding
  • Having to change your sanitary products every hour or two
  • Passing blood clots larger than 2.5cm (around the size of a quarter)
  • Needing two sanitary products at the same time, such as a pad and a tampon
  • More pain than usual

Potential Health Issues

If you noticed that you’re having a heavier flow than normal, either through your own understanding or from the list above, it could be an indication of a health condition such as one of the following.

Uterine Fibroids/Polyps

The most common cause of heavier flows, uterine fibroids and polyps are non-cancerous growths of endometrial or muscular tissue in the wall of your uterus. They can cause a blockage that prevents the uterus from properly contracting, and so they can reduce the flow of blood being expelled by the cervix. Then the blood pools for longer and forms larger clots.

While common and not generally dangerous, these growths can cause other health issues if not managed properly, including:

  • Irregular spotting
  • Feeling bloated
  • Constant lower back pain
  • Pain during sex
  • Fertility issues


Endometriosis means that the endometrium grows somewhere other than your uterus, often in the fallopian tubes and ovaries. This can cause heavy periods, though it more often results in painful ones.

This condition occurs over the course of each menstrual cycle, though the symptoms can grow worse as you start your period. The symptoms can include:

  • Painful periods
  • Heavy periods
  • Nausea, vomiting, and diarrhea during your period
  • Cramping and pain in the lower back and pelvis
  • Pain or discomfort during sex
  • Fertility issues


This condition is when the uterine lining grows into the muscular wall of the uterus itself. This can cause both the endometrium and the uterus to grow larger and thicker, which can cause a heavier flow, and also more and larger clots.

Hormonal Imbalances

The growth of the endometrium over the course of each cycle is governed by a balance of estrogen and progesterone. If these hormones are out of balance, then it can cause a heavy period. This can be caused by being in or about to begin menopause. Stress or a significant gain or loss of weight are frequent triggers too. The most noticeable symptom is irregular or missing periods.


Up to half of all pregnancies result in a miscarriage, often before the woman is even aware that she has conceived. A failed pregnancy normally results in a heavier period, as well as more clotting and cramping.

An Enlarged Uterus

After a pregnancy has come to term, the extra space made to accommodate the little one can often stick around. This gives more room for blood to pool, and so increases the amount of clotting that happens before it is expelled.

Bleeding Disorders

If you suffer from a bleeding disorder such as von Willebrand’s disease (VWD), or a platelet function disorder, this could be the cause of frequent heavy periods. While VWD is a rare condition, it affects between 5 and 24 percent of women who have chronically heavy menstruation.

Waiting for the Painters to Leave

While it’s probably not the most pleasant part of an already trying time, you generally shouldn’t be worried if you have blood clots during your period. What it means most of the time is just that you are in the first few days of your flow. However, if you are regularly getting unusually large clots, along with more pain than usual, you should have a word with your doctor so they can check that it’s not caused by an underlying condition.