Heavy menstrual bleeding is one of the most common gynecological complaints, and it has a surprisingly specific definition: losing more than 80 milliliters of blood per cycle, or needing to change a pad or tampon more often than once an hour. If you’re passing blood clots the size of a quarter or larger, that’s another reliable sign your bleeding has crossed from heavy-but-normal into something worth investigating. The causes range from benign growths in the uterus to hormonal imbalances to blood disorders, and most of them are treatable once identified.
How to Tell If Your Bleeding Is Abnormally Heavy
Period flow varies enormously from person to person, which makes it hard to know when yours has become a problem. Three practical markers help distinguish heavy periods from truly excessive bleeding. First, clot size: clots one inch or larger in diameter (roughly the size of a US quarter) are a red flag. Second, frequency of pad or tampon changes: soaking through one every hour, sometimes called “flooding,” signals heavy blood loss. Third, the bleeding’s impact on your daily life, including fatigue, shortness of breath, or feeling lightheaded, which point to iron loss.
A pictorial blood assessment chart, where you record how many pads or tampons you use and how saturated they are, can help you and your doctor put a number on your flow. Even without a chart, tracking clot size and how often you change protection gives you concrete information to bring to an appointment instead of trying to guess whether your period is “too much.”
Fibroids: The Most Common Structural Cause
Uterine fibroids are noncancerous growths in the wall of the uterus, and they are remarkably common. By age 35, about 60% of Black women and 40% of white women have them, and those numbers climb to over 80% and nearly 70% by age 50. Most fibroids cause no symptoms at all, but in up to 40% of people who have them, they trigger heavy menstrual bleeding.
The reason fibroids cause so much bleeding comes down to blood vessels. As a fibroid grows, it develops a dense network of chaotic, structurally weak blood vessels around it, similar to the blood supply that feeds a tumor. These fragile vessels are prone to breaking and leaking. Fibroids can also physically press on normal blood flow in the uterus, creating enlarged pools of blood (called venous lakes) within the uterine lining that shed heavily during your period. The location of the fibroid matters: those that grow into or just beneath the lining tend to cause the worst bleeding, while those on the outer surface of the uterus may cause no bleeding changes at all.
Hormonal Imbalances and Perimenopause
Your uterine lining thickens each month under the influence of estrogen, then sheds when progesterone drops. When those two hormones fall out of balance, the lining can grow excessively thick and produce a much heavier period when it finally sheds. This is sometimes called estrogen dominance, and it happens when your body produces estrogen without enough progesterone to keep the lining in check.
Perimenopause is the most common time for this to happen. As ovulation becomes irregular in the years before menopause, progesterone production drops off while estrogen can fluctuate wildly. The result is months where the lining builds and builds without the normal progesterone signal to stop. When bleeding does come, it can be unpredictable in timing and far heavier than what you’re used to. This pattern can start as early as your late 30s or early 40s, and it often catches people off guard because they don’t associate heavy bleeding with the approach of menopause.
Other hormonal causes include thyroid disorders, polycystic ovary syndrome, and any condition that disrupts regular ovulation. Even chronic stress can interfere with ovulation enough to shift the estrogen-progesterone balance.
Polyps, Adenomyosis, and Other Uterine Causes
Endometrial polyps are small, finger-like growths on the uterine lining. Like fibroids, they’re usually benign, but they create extra surface area that bleeds during your period. Adenomyosis is a condition where tissue that normally lines the uterus grows into the muscular wall instead. This makes the uterus enlarged and boggy, leading to heavy, painful periods. Endometrial hyperplasia, an overgrowth of the lining itself, can also cause heavy bleeding and is sometimes a precursor to uterine cancer, which is why persistent heavy bleeding in people over 45 typically gets a biopsy.
Blood Disorders and Medications
Not all heavy bleeding originates in the uterus. Von Willebrand disease, an inherited condition that impairs the blood’s ability to clot, affects roughly 1% of the population and disproportionately shows up as heavy periods. Many people with this condition go undiagnosed for years because heavy periods get normalized. If your bleeding has been heavy since your very first period, or if you also bruise easily, have frequent nosebleeds, or bleed excessively after dental work, a clotting disorder is worth investigating.
Medications can also shift your bleeding pattern significantly. Blood thinners reduce your body’s clotting ability, which naturally extends to menstrual blood. The copper IUD is another well-known cause. Unlike hormonal IUDs, which tend to lighten periods, copper IUDs increase menstrual bleeding for many users, and this is one of the most common reasons people have them removed.
How Heavy Bleeding Gets Diagnosed
A workup for heavy bleeding starts with a detailed history: when it started, how much you’re bleeding, your cycle pattern, and any other symptoms. A standard gynecological exam comes next, followed by blood tests to check your hemoglobin and ferritin levels. Hemoglobin tells your doctor whether you’re anemic right now; ferritin reveals whether your iron stores are depleted, which can happen even before your hemoglobin drops into the anemic range.
For identifying structural causes, a transvaginal ultrasound is the first-line imaging test. It can spot fibroids and measure the thickness of your uterine lining, but it can’t always distinguish between polyps, submucous fibroids, and adenomyosis. If the ultrasound is inconclusive or shows something that needs a closer look, the next step is saline infusion sonography, where a small amount of sterile saline is injected into the uterus to create a clearer picture of the cavity. Hysteroscopy, where a tiny camera is inserted through the cervix, is reserved for cases where those earlier tests suggest something inside the cavity that needs direct visualization or removal.
Testing for clotting disorders is typically considered only after structural causes have been ruled out.
When Heavy Bleeding Drains Your Iron
Chronic heavy periods are the leading cause of iron deficiency anemia in premenopausal people. Every cycle, you lose iron along with blood, and if the loss outpaces what you absorb from food, your stores gradually empty. The standard hemoglobin range for adult women is 11.6 to 15.0 grams per deciliter. Dropping below that range means you’re anemic, but you can feel the effects well before you hit that threshold. Fatigue, brain fog, shortness of breath during exercise, pale skin, brittle nails, and feeling cold all the time are classic signs.
Low ferritin is often the earliest indicator. Your body pulls from its iron reserves to keep hemoglobin levels stable, so ferritin can plummet while your hemoglobin still looks normal on a blood test. If you have heavy periods and feel persistently exhausted, asking specifically for a ferritin test (not just a standard blood count) can catch the deficiency earlier.
Signs That Need Immediate Attention
Most heavy bleeding develops gradually over months or years, but certain patterns signal an emergency. Soaking through a pad or tampon every hour for two to three consecutive hours requires prompt medical evaluation. Bleeding heavy enough to cause weakness, dizziness, or fainting means your blood volume is dropping faster than your body can compensate, and that needs same-day attention. Sudden, unusually heavy bleeding outside your normal cycle, especially if you could be pregnant, also warrants urgent care, as it can indicate a miscarriage or ectopic pregnancy.