Period blood clots are jelly-like clumps of blood and tissue that range from bright red to dark red or even blackish, and they’re completely normal in most cases. They can look like thick, gel-like blobs or slightly firm chunks, and they vary in size from a few millimeters to about the size of a quarter. Your body’s uterine lining sheds gradually during your period, and sometimes pieces of that tissue come out as visible clots mixed with blood.
What Normal Clots Look Like
A typical menstrual clot is a small, dense piece of tissue with a jelly-like or slightly rubbery texture. Most are dark red, maroon, or sometimes nearly black, especially if the blood sat in your uterus or vagina before passing. They can also be bright red during heavier flow days. The texture sets them apart from regular liquid blood: they hold together, feel slippery, and don’t dissolve immediately when you touch them.
Clots around the size of a dime or quarter are common and not a concern for most people. You’ll typically notice them on your heaviest days, often day one or two of your period, and they may appear on a pad, in the toilet, or on toilet paper. Some people pass a few small clots every cycle without issue, while others rarely see them at all. Both patterns are normal.
Why Clots Form During Your Period
Your uterine lining thickens each cycle in preparation for a potential pregnancy. When that pregnancy doesn’t happen, the lining breaks down and sheds as your period. Your body produces natural anticoagulants (blood-thinning substances) to keep this blood flowing smoothly. But on heavier days, when blood is leaving the uterus faster than those anticoagulants can work, the blood pools and coagulates into clots before passing through.
This is why clots show up most often during the heaviest part of your period. It’s simply a matter of flow speed outpacing your body’s ability to keep the blood liquid. Overnight clots are also common because blood collects in the uterus while you sleep and then passes in a clump when you stand up.
When Clots Signal a Problem
Size and frequency are the two things that matter most. The CDC considers clots the size of a quarter or larger a sign of heavy menstrual bleeding. Passing golf ball-sized clots, or passing large clots every couple of hours, moves well beyond the normal range.
Other signs that your bleeding is too heavy include:
- Needing to change your pad or tampon every one to two hours for several hours in a row
- Periods lasting longer than seven days
- Soaking through one or more pads or tampons per hour
For reference, a typical period involves about two to three tablespoons of blood loss total over four to five days. Heavy menstrual bleeding usually means losing roughly twice that amount over seven or more days.
Conditions That Cause Large or Frequent Clots
Several underlying conditions can increase clot size and frequency. Fibroids, which are noncancerous growths in the uterine wall, are one of the most common causes. They can distort the uterus and increase the amount of lining that builds up each cycle. Endometriosis and adenomyosis, where uterine-like tissue grows in places it shouldn’t, also contribute to heavier flow and more clotting.
Polycystic ovary syndrome (PCOS) can cause irregular, heavy periods that produce larger clots when they do arrive. Pelvic inflammatory disease, hormonal imbalances, and bleeding disorders like Von Willebrand disease are other possibilities. Certain medications, including blood thinners, can also increase menstrual clotting. In rare cases, heavy periods with large clots can be a sign of uterine cancer.
Decidual Casts vs. Regular Clots
If you pass something that looks like a large piece of raw meat shaped roughly like a triangle or upside-down pear, it may be a decidual cast rather than a typical clot. A decidual cast happens when the entire uterine lining sheds in one piece instead of breaking apart gradually. They’re usually red or pink, fleshy in texture, and about the size of a walnut or small lime, though some are as large as a palm.
Decidual casts are rare and can be extremely painful because a large piece of tissue is passing through the cervix all at once. They often come with severe cramping, pelvic pain, nausea, or dizziness. While they’re not always dangerous, they look alarming and are worth bringing up with a healthcare provider to rule out other causes.
Signs of Anemia From Heavy Periods
If you’re regularly passing large clots and dealing with heavy periods cycle after cycle, your body may not be replacing lost iron fast enough. Iron deficiency anemia is a common consequence, and its symptoms can creep up gradually enough that you might not connect them to your period.
Watch for persistent fatigue and weakness that doesn’t improve with rest, pale skin, cold hands and feet, dizziness or lightheadedness, shortness of breath with normal activity, or a fast heartbeat. Some people develop brittle nails, restless legs, or unusual cravings for ice, dirt, or other non-food items. These cravings sound strange, but they’re a well-documented symptom of iron deficiency and a strong signal that your iron stores are depleted.
If heavy clotting is your norm and you recognize several of these symptoms, a simple blood test can confirm whether your iron levels are low.