Small blood clots during your period are normal, and most people pass them at some point. Clots become a concern when they’re consistently larger than a quarter (about 2.5 cm across) or when they come with bleeding heavy enough to soak through a pad or tampon every hour or two. If your clots are small, dark red or purplish, and only show up on your heaviest days, that’s your body doing exactly what it’s supposed to do.
Why Periods Produce Clots
Each month, your uterus builds up a lining rich with blood vessels to prepare for a possible pregnancy. When that lining sheds, it releases blood into the uterus faster than your body can keep it liquid. Normally, your uterus produces its own natural blood-thinning substances that break down the tissue and keep menstrual blood flowing smoothly. But on heavier days, especially during the first day or two of your period, blood can pool in the uterus or vagina before it exits. When blood sits still long enough, it clumps together into the jelly-like clots you see on your pad or in the toilet.
This is why clots are most common when you wake up in the morning or stand up after sitting for a while. Blood has been collecting while you were still, and it passes all at once. The clots themselves are a mix of blood cells, tissue from the uterine lining, and proteins involved in clotting. Their color ranges from bright red to deep burgundy depending on how long the blood sat before leaving your body.
When Clots Signal a Problem
The CDC uses a quarter-sized clot as the threshold for concern. Passing one large clot once in a while may not mean much, but regularly seeing clots that size or bigger is one of the hallmarks of heavy menstrual bleeding. Doctors define heavy periods as losing more than 80 milliliters (roughly 2.7 ounces) of blood per cycle, though that’s nearly impossible to measure at home.
More practical signs that your bleeding is too heavy:
- Pad or tampon changes every one to two hours for several hours in a row
- Needing to double up on pads and tampons at the same time
- Periods lasting longer than seven days
- Frequent large clots throughout your period, not just on day one
- Feeling exhausted, dizzy, or short of breath around your period, which can point to iron-deficiency anemia from chronic blood loss
If you’re soaking through at least one pad or tampon per hour for more than two consecutive hours, that warrants prompt medical attention rather than waiting for a scheduled appointment.
What Causes Heavy Clotting
Hormonal Imbalances
Your uterine lining grows in response to estrogen during the first half of your cycle, then stabilizes and eventually sheds when progesterone drops. If you don’t ovulate in a given cycle (which happens more often than most people realize, especially during perimenopause, adolescence, or with conditions like PCOS), progesterone never kicks in to counterbalance estrogen. The lining keeps thickening unchecked, and when it finally breaks down, there’s simply more tissue and blood to shed. The result is a heavier, clottier period.
This pattern of “unopposed estrogen” can also lead to a condition called endometrial hyperplasia, where the lining becomes abnormally thick. Most people with this condition notice increasingly heavy periods with clots, and sometimes bleeding between periods as well.
Fibroids and Polyps
Uterine fibroids are noncancerous growths in the muscle wall of the uterus, and they’re one of the most common structural causes of heavy, clotty periods. Fibroids contribute to heavy bleeding through several mechanisms. They increase the surface area of the uterine lining, meaning more tissue builds up and sheds each month. They can also compress surrounding blood vessels, creating enlarged, dilated veins that bleed more heavily and resist the body’s normal clotting process. The blood vessels that supply fibroids tend to be structurally irregular and fragile, making them prone to breaking and bleeding more than normal uterine vessels.
Fibroids also interfere with the uterus’s ability to contract and squeeze blood vessels shut after the lining sheds, which is one of the body’s key ways of controlling menstrual blood loss. Polyps, which are smaller growths on the uterine lining itself, can cause similar symptoms on a smaller scale.
Other Causes
Adenomyosis, where uterine lining tissue grows into the muscular wall of the uterus, often produces heavy bleeding and painful clots. Bleeding disorders that affect how well your blood clots throughout your body (not just during your period) can also be a factor. Thyroid problems, certain medications including blood thinners, and copper IUDs can all increase menstrual flow and clotting as well.
How Heavy Clotting Affects Your Health
The biggest day-to-day risk of chronically heavy periods is iron-deficiency anemia. Every period depletes your iron stores, and if you’re losing more blood than average, your body may not be able to replenish iron fast enough between cycles. The symptoms creep up gradually: persistent fatigue, weakness, dizziness, shortness of breath during activities that didn’t used to wind you, and sometimes pale skin or brittle nails. Many people attribute this to stress or poor sleep without connecting it to their periods.
A simple blood test measuring your hemoglobin level and ferritin (a protein that reflects your iron stores) can reveal whether your periods are taking a measurable toll. Low ferritin can cause fatigue and brain fog even before your hemoglobin drops low enough to officially qualify as anemia.
What to Expect at the Doctor
If you bring up heavy clotting, your doctor will likely start with blood work to check your iron levels, thyroid function, and sometimes clotting factors. A transvaginal ultrasound is typically the first imaging test, since it can identify fibroids, polyps, and other structural issues without any invasive procedure.
If the ultrasound is inconclusive, a saline infusion sonography (where a small amount of fluid is used to expand the uterus during ultrasound for a clearer view) or a hysteroscopy (a thin camera inserted through the cervix) may follow. Hysteroscopy has the advantage of allowing your doctor to both see and potentially remove small polyps or fibroids during the same visit. For people over 45, or when the lining looks unusually thick on imaging, an endometrial biopsy may be recommended to rule out precancerous changes.
One tool you can use before your appointment is a pictorial blood assessment chart, which involves recording how many pads or tampons you use each day and how soaked they are. A standardized version of this chart correlates well with actual measured blood loss and gives your doctor concrete information to work with rather than a subjective description of “heavy.”
Treatment Options
Treatment depends on the underlying cause. Hormonal options, such as birth control pills, hormonal IUDs, or other progesterone-based treatments, work by thinning the uterine lining so there’s less to shed each month. For many people, a hormonal IUD dramatically reduces both flow and clotting within a few months.
Medications that help your blood clot more effectively can reduce bleeding by 30 to 50 percent during your period. Anti-inflammatory pain relievers also have a mild effect on reducing menstrual flow, which is why they’re sometimes recommended for the first few days of your period beyond just pain relief.
When fibroids or polyps are the cause, removing them often resolves the heavy bleeding. Depending on size and location, this can range from a minimally invasive procedure through the cervix to a more involved surgery. For people who are done having children and haven’t found relief with other treatments, procedures that remove or destroy the uterine lining, or in some cases hysterectomy, are options that provide permanent resolution.
Iron supplementation is important for anyone whose levels are low, regardless of what other treatment they pursue. Rebuilding depleted iron stores can take several months, and many people are surprised by how much better they feel once their levels normalize.