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Illustration by Katrin Friedmann

Reading time: 6 min

Blood clots during your period: what are they?

Top things to know about period blood clots:

  • Period bleeding varies cycle to cycle

  • You can expect blood clots during the heaviest days of your period

  • Blood clots often form if blood builds up in your uterus or vagina before exiting

  • If you have clots larger than about an inch or 25 mm long it's a good idea to talk with your healthcare provider

Are period blood clots typical?

Have you ever wondered what exactly is in your tampon, cup, or pad? Throughout your period, you will bleed about 2-3 tablespoons (35-45 ml) of blood. This includes the uterine lining, which is made of cells similar to skin cells, blood vessels, and glands (6). Every period is unique (4) and each varies in frequency, heaviness, color, and texture. Clots or clumps on the heaviest days of a period may be typical for some people. Period blood clots can appear like clumps or chunks of blood, and/or a jelly-like consistency and can vary in size and number.

It's a good idea to talk with your healthcare provider if you have clots that are 1 inch (24.5 mm) in length or larger (1).

What does period blood look like?

Blood and discharge change in color and consistency during your menstrual cycle. Newer blood will be free-flowing and bright red. Heavier bleeding will appear darker and thicker. As your period is coming to an end, it may start to thin and turn to a lighter pink, brown, or yellow color. 

Blood may look a little orange if it is mixed with cervical fluid. Cervical mucus (discharge) may look a little jelly-like (5). If the blood is an orange color, it can also be a sign of an untreated infection. If you have orange blood often or if you have gray or green discharge, you should contact your doctor or midwife, because you may have an infection (5). Other signs of infection are pain, itching, or a bad vaginal odor that could smell “fishy” (5).

Darker blood is usually seen with heavy bleeding. Conditions like polycystic ovarian syndrome (PCOS) or endometriosis can cause the uterine lining to be thicker before shedding (4, 8). This can make the blood look a purplish color (1, 4). Blood may look black if it sat in the uterus or vagina for a while. This can happen at the beginning or end of a period or could be related to a blockage. Very dark, heavy bleeding that looks gritty or has a lot of clumps could be a sign of a miscarriage or another condition (3). Contact your healthcare provider if you have very dark blood with a sudden onset of heavy bleeding and cramping, or with new pain, fever, or bad smell (3, 5). 

Period blood clots can be thick and lumpy or stringy. They form if blood builds up in the uterus before exiting the cervix or in the back of the vagina. Blood clots are also linked to fibroids - non-cancerous growths on the uterus (4).

Periods may be thin and watery if the hormone estrogen is low. This can happen during life stages, such as breastfeeding or perimenopause. It can also happen because of extreme exercise, weight loss, or malnourishment (3).

Each person’s period will be unique. Your periods may look different than someone elses and may have slight differences cycle to cycle. If you see big changes in your periods, it’s a good idea to talk to your healthcare provider.

Are you using Clue to track your bleeding patterns? Download the app and start today

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Is my period bleeding “heavy”?

Heavy period bleeding is common. This doesn’t mean you should just live with it, because it can have negative impacts on your health. That is why healthcare providers call it “abnormal uterine bleeding” (3). Heavy bleeding includes any of the following (1):

  • Soaking one or more tampons or pads in an hour for two or more hours

  • Clots larger than a quarter (1 in or 24.5 mm)

  • Vaginal bleeding lasting longer than 7 days

  • Needing to change pad/tampon/cup during the night

  • Needing to wear more than one pad at a time

What causes heavy bleeding? 

Unpredictable bleeding during your menstrual cycle could be related to some reproductive health conditions(2, 4, 7):

  • Unpredictable ovulation: The uterine lining can thicken if ovulation doesn’t happen as frequently as your body needs. During and around the times of menarche (the first period) and menopause, it’s common to experience unpredictable bleeding. Polycystic ovary syndrome (PCOS) and hypothyroidism are also related to unpredictable bleeding. 

  • Fibroids or polyps: Growths on the uterus that are normally not cancerous but may require followup with a healthcare provider to monitor blood loss. 

  • Adenomyosis: Where the lining of the uterus grows into the uterus muscle.

  • Endometriosis: Where the uterus lining grows on other pelvic organs, like the ovaries or fallopian tubes.

  • Medications: Some forms of birth control, like the intrauterine device (IUD) may cause heavier bleeding the first year of use, but many people find bleeding is reduced after that time. Blood thinners like aspirin may thin blood and cause heavier bleeding.

  • Bleeding disorders: Blood may not clot as the body needs it to in some bleeding disorders like Von Willebrand disease.

  • Cancer: Endometrial (lining of the uterus) cancer. Most endometrial cancer is found in women in their mid-60s.

  • Pelvic Inflammatory disease (PID): Infection of the uterus, fallopian tubes, or ovaries usually caused by an untreated sexually transmitted infection (STI). 

  • Ectopic pregnancy: Pregnancy that begins growing outside of the uterus, usually in a fallopian tube.

  • Miscarriage: A death of an embryo or fetus before it can live outside of the uterus.

When to see your healthcare provider for heavy bleeding

Consider talking  to your healthcare provider if you see any of the following (1, 3):

  • No period bleeding for 3-6 months

  • Bleeding or spotting in between periods

  • Soaking one or more pads/tampons every hour

  • Bleeding for longer than 7 days

  • Bleeding or spotting after sex

  • Blood clots larger than the size of a quarter 

  • Large grayish clots 

  • Any changes that see out of the normal for your period

Consider seeking emergency care if you:

  • Feel lightheaded, dizzy,  short of breath, or experience chest pain related to period bleeding 

For some people, blood clots are most common on the heaviest days of their period. If you experience heavy period bleeding and are worried, you should consider talking with a healthcare provider. Even if you do not have the symptoms in this article, being worried is reason enough to check in with your healthcare provider. Consider talking with your friends about your periods, because sharing what each of your period blood looks like and how it changes cycle to cycle may bring reassurance to you all. You may see that what you're experiencing is similar to your friends' experiences too. 

Download Clue to track your bleeding and symptoms during your period to better understand what is normal for you, and to spot any changes. 

An original version of this article was published September 27th 2017.

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