What Causes Period Blood Clots and How to Stop Them

What causes period blood clots during your cycle?

First, a mini-primer on blood clots in general. When you think about clots of blood, you might imagine the kind that come together when you have a cut. Your body springs into action, combining enough platelets (blood cells that adhere to each other) and proteins from plasma (the liquid part of your blood) to plug the injured blood vessel¹. This is how clots help to stop bleeding.

Blood can also clot in your veins, especially if you have risk factors like being pregnant, which causes hormone changes that increase your blood clot risk, or recently having surgery, because moving less also contributes to this health hazard. These clots can dissipate without harm, but sometimes they can be life-threatening.

The blood clots that can emerge from your vagina during your period are a bit different than these other types, though. Menstrual blood clots are comprised of the endometrial lining that builds up in your uterus in preparation for pregnancy, then sloughs off during your period when you don’t conceive.

“Clots are normal, but they typically happen when a [person] has a heavy flow,” G. Thomas Ruiz, M.D.², lead ob-gyn at MemorialCare Orange Coast Medical Center in Fountain Valley, California, tells SELF.

This is in part because a gushing period prompts your body to form clots so you don’t lose more blood than you should (around two to three tablespoons over the course of your entire period). Also, the opening of your cervix (the narrow passage at the lower end of your uterus) is pretty small. If you have a substantial flow, that allows the blood to build up in your uterus, Dr. Ruiz explains, giving components like platelets and plasma proteins time to congeal.

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How big should period clots be?

For the most part, period clots are a completely normal part of menstruation, Mary Jane Minkin, M.D.³, a clinical professor of obstetrics and gynecology and reproductive sciences at Yale Medical School, tells SELF.

But if you’re seeing clots the size of a quarter or larger, you should visit your doctor, according to the Centers for Disease Control and Prevention (CDC)⁴.

“If someone is passing quarter-size clots, that tells me that there could be something wrong [in] the uterus that needs further investigation,” Dr. Ruiz says. You can even take a picture of what you’re seeing so that your doctor can look during your visit. “It helps show me the magnitude of what’s been going on,” Dr. Ruiz says.

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When should I be concerned about blood clots during my period?

Period clots the size of a quarter or larger actually indicate that you’re officially in heavy bleeding territory, also known as menorrhagia. According to the CDC, other menorrhagia symptoms include:

1. You’re soaking through one or more tampons or pads every hour for multiple hours in a row.
2. You need to use two pads at a time.
3. You have to change your pad or tampon during the night.
4. You bleed for more than seven days.
5. Your flow is so heavy that it sometimes prevents you from living your normal life.
6. You regularly experience pelvic pain (especially in your lower abdomen) during your period.
7. You’re constantly fatigued.

The reason why all of this matters (other than making your life borderline hell during your period): Having heavy, drawn-out bleeding can lead to anemia, a blood issue that can leave you feeling tired or weak, the CDC says. It can also be a sign of an underlying health condition that requires treatment (but more on that in a sec).

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OK, are large blood clots ever normal during your period?

It’s important to remember that “normal” is a relative term for everyone, Christine Greves, M.D.⁵, a board-certified ob-gyn at the Winnie Palmer Hospital for Women and Babies, tells SELF. If your usual is to pass occasional larger clots, then that may simply be your usual, as long as you are not anemic and your quality of life is not affected, she explains.

Meaning, if you’ve always had one period clot that you’re tempted to take a photo of or pester your best friend about every month, but you otherwise feel OK and aren’t soaking through tampons or pads like it’s your job, it’s probably nothing to be too stressed about. Still, Dr. Greves says, it’s not a bad idea to bring it up during your next check-up with your ob-gyn, just to get their take. And, remember, if you’re bleeding heavily, are in pain, or have any other symptoms of menorrhagia, you should get it addressed sooner rather than later.