Small blood clots during your period are normal for most people. Clots the size of a dime or even a quarter can show up during heavier flow days, and they’re usually nothing to worry about. Passing clots that are larger than a quarter, or passing them frequently throughout the day, is where things shift from typical to worth investigating.
What Period Clots Actually Are
Period clots aren’t the same as the blood clots that form in a vein or artery. Those clots are made of fibrin, a protein your body uses to stop bleeding from wounds. Menstrual clots are different. Research published in the American Journal of Obstetrics and Gynecology found that period clots are actually clusters of red blood cells held together by mucus-like substances, not fibrin at all. Fibrinogen, the precursor to fibrin, is absent from menstrual discharge entirely.
Your uterine lining contains enzymes that break down blood as it’s shed, keeping it liquid so it flows out easily. On heavier days, when blood is leaving the uterus faster than those enzymes can work, some of it pools and clumps together, often in the vagina, before passing out of the body. That’s why clots tend to appear on your heaviest days (usually day one or two of your period) and disappear as your flow lightens.
Normal Clots vs. Clots Worth Checking
The size and frequency of your clots matter more than whether they show up at all. Clots the size of a dime or quarter during your heaviest days fall within the normal range. The CDC flags clots the size of a quarter or larger as a sign of heavy menstrual bleeding. If you’re regularly passing clots the size of a golf ball, or passing large clots every couple of hours, that’s a pattern to bring to your doctor’s attention.
Other signs that your clotting may signal something more:
- Soaking through a pad or tampon every hour for several consecutive hours
- Periods lasting longer than 7 days
- Needing to change protection overnight to avoid leaking
- Feeling exhausted, dizzy, or short of breath during or after your period
A normal cycle involves roughly 25 to 80 mL of blood loss total, which is about 2 to 5 tablespoons over the entire period. Losing more than 80 mL per cycle is the clinical threshold for heavy menstrual bleeding.
What Clot Color Tells You
The color of your clots reflects how quickly blood is leaving your body, not how healthy or unhealthy the blood is. Bright red clots form from fresh blood flowing steadily during peak flow days. Dark red or maroon clots have sat in the uterus a bit longer before passing. Brown or nearly black clots are older blood that oxidized while waiting to be shed, which is most common at the very beginning or tail end of your period when flow is slowest.
None of these colors on their own indicate a problem. Pink-tinged blood is simply blood mixed with cervical fluid, common on lighter days. The color can change from hour to hour on the same day, depending on how quickly your uterus is shedding.
Conditions That Cause Heavy Clotting
When clotting is persistently heavy cycle after cycle, there’s usually an underlying reason. The most common causes fall into a few categories.
Hormonal Imbalance
Your uterine lining builds up each cycle in response to estrogen, then sheds when progesterone drops. If estrogen runs high without enough progesterone to balance it, the lining grows thicker than usual, producing a heavier, clottier period when it finally sheds. This is especially common during two life stages: the first few years after periods begin, when hormonal patterns are still stabilizing, and perimenopause, when cycles become irregular and ovulation is less consistent. Both situations can lead to cycles where the lining builds up excessively before shedding.
Uterine Fibroids and Polyps
Fibroids are noncancerous growths in the muscular wall of the uterus. They can distort the uterine cavity, increasing the surface area that bleeds during a period. Polyps are smaller growths that attach to the uterine lining by a base or thin stalk and can grow to several centimeters. Both fibroids and polyps are common and frequently cause heavy flow with large clots, irregular bleeding, or bleeding between periods.
Adenomyosis
In adenomyosis, the tissue that normally lines the uterus grows into the muscular wall of the uterus itself. This causes the uterus to enlarge and bleed more heavily during periods. It’s a frequent cause of painful, clot-heavy periods, particularly in people in their 30s and 40s.
Bleeding Disorders
Conditions like von Willebrand disease, where blood doesn’t clot properly, can make periods significantly heavier. These disorders are sometimes missed for years because heavy periods get dismissed as “just how things are.” If your periods have been very heavy since they first started, or if you also bruise easily or bleed a lot from minor cuts, a bleeding disorder could be a factor.
Medications
Blood thinners can increase menstrual bleeding substantially. Hormonal birth control methods occasionally cause unexpected changes in flow as well, sometimes heavier, sometimes lighter, depending on the type and how your body responds.
Heavy Clotting and Iron Deficiency
Heavy menstrual bleeding is the leading cause of iron deficiency in women of reproductive age. Every period removes iron from your body, and when bleeding is heavy enough to produce large or frequent clots, the losses can outpace what you take in from food.
Iron deficiency doesn’t always show up as dramatic symptoms. It can build gradually over months or years, showing up as fatigue you’ve learned to live with, difficulty concentrating, feeling cold when others don’t, or getting winded going up stairs. A ferritin level below 30 ng/mL generally indicates iron deficiency, and your body’s iron absorption doesn’t fully normalize until ferritin reaches about 50 ng/mL. If your periods are consistently heavy, checking your iron levels gives you a clear, actionable number to work with.
What to Expect at the Doctor
If your clotting pattern raises concerns, a doctor will typically start with blood work to check for anemia and iron levels, along with an ultrasound to look at the structure of your uterus. These two steps can identify or rule out fibroids, polyps, adenomyosis, and signs of hormonal imbalance. If a bleeding disorder is suspected, specialized blood tests can evaluate how well your blood clots.
Tracking your periods before your appointment makes the conversation more productive. Note how many days you bleed, how often you change your pad or tampon, whether you pass clots, and roughly how large they are. Comparing clots to coins (dime, quarter, half-dollar) gives your doctor a quick, useful reference point. Many people underestimate or overestimate their flow without these concrete details, so even a few cycles of tracking helps.