Why Am I Getting So Many Blood Clots On My Period?

Menstrual blood contains clots because your body releases anticoagulants to keep period blood from clotting inside the uterus. When bleeding is heavy or fast, those anticoagulants can’t keep up, and clots form. Seeing occasional clots — especially on your heaviest days — is normal. Seeing many large clots regularly is not, and it’s worth finding out why.

Clots are one of the most reliable signals that something about your period has changed. They tell you about flow volume, not just flow duration. A period can last a normal number of days and still produce concerning clots if the volume is high. That distinction matters because heavy bleeding is common, underreported, and treatable.

What Causes Blood Clots During a Period?

During menstruation, the uterus sheds its lining. That tissue breaks down and mixes with blood. To keep this mixture liquid enough to pass through the cervix, the body releases anticoagulant proteins — primarily plasmin — into the menstrual fluid. These proteins break down fibrin, the mesh-like protein that forms clots.

When bleeding is light to moderate, the anticoagulants keep pace. The blood stays thin and flows out. When bleeding is heavy, the volume of blood overwhelms the available anticoagulants. Fibrin forms faster than it can be broken down. The result is clots.

This is a mechanical explanation, not a disease process on its own. Clots are a symptom of flow rate. The question is always why the flow rate is high.

Clot size gives useful information. Clots smaller than a dime are common and generally not concerning. Clots larger than a quarter — roughly the size of a quarter in diameter — suggest heavy bleeding that warrants medical evaluation. Some clinicians use the threshold of a golf ball or larger as clearly abnormal. The exact size cutoff varies by source, but the principle is consistent: larger clots mean heavier flow.

Why Am I Getting So Many Blood Clots On My Period Suddenly?

A sudden change in clotting pattern is different from a lifelong pattern. If your periods have always produced some clots and nothing has changed, that’s one situation. If clots appeared recently, increased in size, or increased in number after years of lighter periods, that’s another — and it deserves attention.

Several things can cause a sudden shift:

• Hormonal changes. Shifts in estrogen and progesterone can thicken the uterine lining, which means more tissue to shed and heavier bleeding. This can happen during perimenopause, after stopping hormonal birth control, or with thyroid changes.
• Uterine fibroids. These noncancerous growths in the uterine wall can increase the surface area of the lining and interfere with normal contraction of the uterus. Both effects increase bleeding.
• Endometrial polyps. Small growths on the uterine lining can cause irregular and heavy bleeding.
• Adenomyosis. Endometrial tissue growing into the muscular wall of the uterus can cause heavy, painful periods. It’s more common in women over 35 who have had children, though it can occur earlier.
• Pregnancy-related causes. A miscarriage or ectopic pregnancy can cause sudden heavy bleeding with clots. If there’s any chance you could be pregnant, this needs urgent evaluation.
• Bleeding disorders. Conditions like von Willebrand disease affect how blood clots. They’re present from birth but may only become obvious when menstrual bleeding is heavy. Some estimates suggest a meaningful share of women with heavy periods have an underlying bleeding disorder, though how common this is depends on the population studied.
• Medications. Blood thinners, including aspirin at higher doses and anticoagulant drugs, can increase menstrual bleeding.
• Infection. Pelvic inflammatory disease or other uterine infections can cause irregular bleeding, though clots are not the primary symptom.

The word “suddenly” is doing a lot of work here. If the change happened over one or two cycles, the list above is a reasonable starting point. If it happened over a year, hormonal shifts and structural causes like fibroids become more likely. Either way, a clinician can narrow it down.

How Much Bleeding Is Too Much?

Heavy menstrual bleeding has a clinical definition. It’s bleeding that interferes with your daily life — not just volume, but impact. The formal criteria include:

• Bleeding that lasts more than 7 days
• Soaking through one pad or tampon every hour for several consecutive hours
• Passing clots larger than a quarter
• Needing to double up on protection (pad plus tampon)
• Waking up at night to change protection
• Bleeding that limits work, exercise, or social activities

These criteria come from established gynecological practice and are used in clinical settings. They’re not perfect — some women with objectively heavy bleeding don’t feel it interferes with their lives, and some with moderate bleeding feel significantly affected. But they provide a useful benchmark.

One non-obvious point: the total volume of menstrual blood in a typical period is roughly 30 to 80 milliliters. That’s about 2 to 5 tablespoons. Heavy bleeding is generally defined as more than 80 milliliters per cycle. Most people dramatically overestimate how much they’re losing and underestimate what’s normal. If you’re soaking through protection every hour, you’re likely well above that threshold.

When Should I Be Concerned About Blood Clots on My Period?

Size and frequency are the two main factors. Occasional small clots on your heaviest day are common. Recurring large clots, especially multiple clots per cycle, are not.

Seek medical evaluation if you notice:

• Clots larger than a quarter, repeatedly
• Clots accompanied by bleeding that soaks through a pad or tampon every hour for more than two hours
• Clots with severe pain that doesn’t respond to over-the-counter pain relievers
• Clots along with dizziness, fatigue, or shortness of breath — these can signal anemia from blood loss
• Sudden onset of heavy clotting after a positive pregnancy test or possible pregnancy
• Clots with fever, unusual discharge, or pelvic pain

Some of these are urgent. Heavy bleeding with dizziness or fainting needs emergency care. Bleeding with a possible pregnancy needs urgent evaluation. The rest warrant a prompt appointment with a gynecologist or primary care clinician.

Iron deficiency anemia is a common consequence of ongoing heavy bleeding. It develops gradually and can cause fatigue, shortness of breath, and pale skin. A simple blood test can check for it. If you’ve had heavy periods with clots for months, it’s reasonable to ask about iron levels even if you feel mostly fine.

What Conditions Are Most Commonly Linked to Heavy Clotting?

The most common structural causes are uterine fibroids and adenomyosis. Fibroids are noncancerous growths that can range from tiny to large enough to distort the uterus. They’re common — research suggests they affect a majority of women by age 50, though many cause no symptoms. When they do cause symptoms, heavy bleeding with clots is one of the most frequent.

Adenomyosis involves endometrial tissue growing into the uterine muscle. It can cause heavy, painful periods and an enlarged uterus. Diagnosis has historically required imaging or tissue examination, though imaging techniques have improved.

Hormonal causes are also common. Anovulatory cycles — cycles where no egg is released — can lead to unopposed estrogen exposure, which thickens the lining. When that lining sheds, bleeding can be heavy and clotty. This is more common at the extremes of reproductive age: in the first few years after menarche and in the years leading up to menopause.

Thyroid disorders can affect menstrual flow. Both hypothyroidism and hyperthyroidism have been associated with changes in bleeding patterns, though the relationship is not always straightforward.

Bleeding disorders deserve specific mention because they’re often missed. Von Willebrand disease is the most common inherited bleeding disorder. It affects roughly 1 in 100 to 1 in 1,000 people, depending on how strictly it’s defined. Many people with it don’t know they have it until they experience heavy menstrual bleeding or bleeding after surgery or childbirth. If you’ve had heavy periods since your teens and they’ve never been explained, a bleeding disorder is worth considering.

What Should I Do About It?

Start by tracking your periods. Note the number of days, how often you change protection, the size of clots, and any pain or other symptoms. This information helps your clinician identify patterns and decide what testing is appropriate.

At your appointment, be specific. “I’m passing clots the size of a quarter several times a day for the first three days” is more useful than “my periods are heavy.” Clinicians rely on details to distinguish between normal variation and something that needs investigation.

Evaluation typically includes a pelvic exam, blood tests to check for anemia and thyroid function, and imaging such as a pelvic ultrasound. Depending on findings, further testing might include a hysteroscopy (looking inside the uterus) or an endometrial biopsy.

Treatment depends on the cause. Hormonal birth control can regulate cycles and reduce bleeding. Non-hormonal medications like tranexamic acid can reduce bleeding during periods. Procedures to remove fibroids or polyps may be options. In some cases, endometrial ablation or hysterectomy is considered. The right approach depends on your symptoms, your goals, and what’s causing the bleeding.

What’s not helpful is waiting indefinitely. Heavy bleeding with clots is common, but common doesn’t mean it should be ignored. It can affect your energy, your iron levels, and your quality of life. And in some cases, it’s a sign of something that needs treatment.