Passing small blood clots during your period is normal. Your body naturally sheds the lining of your uterus each cycle, and when blood pools in the uterus before leaving, it can clot. Most clots are small, dark red or maroon, and nothing to worry about. Clots that are consistently the size of a quarter or larger, though, signal something worth investigating.
How Menstrual Clots Form
During your period, your uterus sheds its inner lining along with blood from small vessels that break open in the process. Your body releases natural anticoagulants to keep menstrual blood liquid so it can flow out easily. But when bleeding is heavy or fast, those anticoagulants can’t keep up. Blood pools in the uterus or vagina, sits long enough to clot, and what comes out looks like a jelly-like mass ranging from bright red to almost black.
This is why clots are more common on your heaviest days, typically the first two days of your period. If blood is leaving your body at a steady, moderate pace, you’re less likely to notice clots at all. The heavier the flow, the more likely clotting becomes.
When Clots Are Considered Abnormal
The CDC defines a concerning sign as menstrual clots the size of a quarter or larger. Other markers of heavy menstrual bleeding include soaking through a pad or tampon every hour for several consecutive hours, bleeding that lasts longer than seven days, or flow heavy enough to interfere with your daily life. A normal period involves 5 to 80 mL of blood loss total, roughly one to five tablespoons across the entire cycle. Anything above 80 mL is classified as heavy menstrual bleeding.
You don’t need to measure your blood loss precisely. If you’re doubling up on protection, waking at night to change pads, or routinely passing large clots, that pattern alone tells you something is off.
Hormonal Imbalances
Estrogen and progesterone work together to build up and then shed your uterine lining each month. When these hormones fall out of balance, the lining can grow too thick. A thicker lining means more tissue to shed and more blood vessels to break open, which leads to heavier bleeding and bigger clots.
This kind of imbalance is common during puberty and perimenopause, when hormone levels naturally fluctuate. It also happens with conditions like polycystic ovary syndrome, thyroid disorders, or long stretches without ovulation. If you’re not ovulating regularly, your body keeps producing estrogen without the counterbalancing progesterone that normally keeps the lining in check. The lining builds and builds until it sheds unpredictably, often in a heavy, clot-filled period.
Fibroids
Uterine fibroids are noncancerous growths in the muscular wall of the uterus, and they’re one of the most common reasons for heavy, clot-heavy periods. They affect a significant number of women, particularly from the 30s onward.
Fibroids cause heavy bleeding through several mechanisms. As they grow, they increase the surface area of the uterine lining, which means more tissue and more blood vessels involved in each period. They also compress surrounding veins, creating dilated, engorged blood vessels that are harder for the body’s clotting system to seal off. The clotting plugs that normally stop bleeding from small vessels simply can’t close off these larger, pressurized vessels effectively. Fibroids can also interfere with the uterus’s ability to contract properly, and those contractions are what helps squeeze blood vessels shut and slow bleeding after the lining sheds.
Adenomyosis
Adenomyosis happens when tissue that normally lines the inside of the uterus grows into the muscular wall itself. This leads to a boggy, enlarged uterus that bleeds more heavily and cramps more painfully than normal. The condition increases the density of tiny blood vessels in the uterine wall and disrupts normal contractions, both of which contribute to heavier flow and larger clots.
Adenomyosis is often confused with fibroids because the symptoms overlap: painful periods, heavy bleeding, and pelvic pressure. It’s also frequently found alongside endometriosis, though the two conditions involve different underlying processes. Adenomyosis is most commonly diagnosed in women in their 30s and 40s, and it tends to resolve after menopause.
Other Possible Causes
Bleeding disorders affect how well your blood clots throughout your body, not just during your period. Conditions like von Willebrand disease can make periods significantly heavier from your very first cycle. Endometrial polyps, small growths on the uterine lining, can also cause irregular or heavy bleeding. Less commonly, heavy menstrual bleeding can be an early sign of changes in the uterine lining that need further evaluation, which is why persistent or worsening symptoms are worth bringing up.
The Iron Deficiency Connection
Heavy periods with frequent clotting don’t just affect your cycle. They can quietly drain your iron stores over months or years. Iron deficiency is one of the most common consequences of heavy menstrual bleeding, and it often goes unrecognized because the symptoms creep up gradually.
Even before you become anemic, low iron can cause fatigue, weakness, difficulty concentrating, and restless legs. Once anemia develops, lightheadedness and shortness of breath during normal activity can follow. If you’ve been passing large clots regularly and feel persistently tired or foggy, low iron is a likely contributor. A simple blood test can check your levels.
What an Evaluation Looks Like
If your clots are large or your bleeding is heavy enough to disrupt your life, the first step is usually a pelvic ultrasound. This imaging can identify structural causes like fibroids, polyps, or signs of adenomyosis. Blood work typically includes a check for anemia and iron levels, along with thyroid function and hormone levels to look for imbalances.
For women 45 and older, or younger women with persistent heavy bleeding that hasn’t responded to treatment, an endometrial biopsy may be recommended. This involves taking a small tissue sample from the uterine lining to rule out abnormal cell changes.
How Heavy Clotting Is Managed
Treatment depends on the cause, but several effective options exist. Hormonal options, particularly a hormonal IUD, are often the first approach. In clinical studies, a hormonal IUD reduced menstrual blood loss by over 90% within three to six months, with about 82% of women meeting the threshold for treatment success. The IUD works by thinning the uterine lining directly, which reduces both the volume of bleeding and the formation of clots.
For women who prefer a non-hormonal option, tranexamic acid is a medication taken only during your period that helps your body’s natural clotting system work more effectively. It reduces menstrual blood loss by 26% to 60% and is taken for four to five days starting on the first day of your cycle. It doesn’t change your hormones or your cycle length. It simply reduces the amount of bleeding.
When fibroids or polyps are the cause, removing or shrinking them often resolves the heavy bleeding directly. The right approach depends on the size, number, and location of the growths, and can range from minimally invasive procedures to surgery.
Tracking What You’re Experiencing
Before any appointment, it helps to track a few cycles. Note how many pads or tampons you use per day, whether you’re soaking through them in under two hours, how many days your period lasts, and the approximate size of any clots. Comparing them to a coin (dime, nickel, quarter) gives your provider a quick visual reference. This kind of detail makes it much easier to figure out what’s going on and how urgently it needs attention.