Heavy periods usually come down to one of a few causes: a hormonal imbalance, a structural change in the uterus, a bleeding disorder, or sometimes a thyroid problem. Clinically, a period is considered heavy when you lose more than 80 milliliters of blood per cycle or bleed for longer than seven days. That threshold sounds abstract, but there are practical ways to gauge it, and understanding the underlying cause is the first step toward getting it fixed.
How to Tell If Your Period Is Actually Heavy
Most people don’t measure their menstrual blood in milliliters, so healthcare providers use real-world indicators instead. Soaking through a pad or tampon every hour for several consecutive hours, passing blood clots larger than a grape, or needing to change protection overnight are all signs your flow is beyond the normal range. Flooding or gushing that disrupts your daily routine also counts.
One widely used tracking method assigns points based on how saturated your pads or tampons are each day. A lightly stained pad scores 1 point, a moderately soiled one scores 5, and a fully saturated pad scores 20. Tampons follow a similar scale, and clots add points too: 1 for small (grape-sized), 5 for large (strawberry-sized). If your total for the cycle exceeds 100, that’s a strong signal to bring it up with a healthcare provider. Tracking even one cycle this way gives you concrete data to share at an appointment, which makes diagnosis much faster.
Hormonal Imbalance Is the Most Common Culprit
Your menstrual cycle depends on a balance between two hormones. Estrogen thickens the uterine lining during the first half of your cycle, building up a cushion that could support a pregnancy. After ovulation, progesterone stabilizes that lining and, if no pregnancy occurs, its drop signals your uterus to shed it as your period.
When you don’t ovulate in a given cycle, progesterone never rises. Without that counterbalance, estrogen keeps building the lining unopposed, making it much thicker than usual. When it finally sheds, there’s simply more tissue and blood to pass. This pattern is especially common during two life stages: the first few years of menstruation, when cycles haven’t fully regulated, and perimenopause, when ovulation becomes irregular. Conditions like polycystic ovary syndrome (PCOS) can also suppress ovulation and create the same effect at any age.
Fibroids and Other Structural Changes
Uterine fibroids are the single most common structural cause of heavy periods. These noncancerous growths develop in the wall of the uterus, and in roughly 30 to 40 percent of people who have them, they cause noticeably heavier bleeding. Fibroids that grow into or distort the inner lining of the uterus tend to cause the worst bleeding because they increase the surface area that sheds each month and can interfere with the uterus’s ability to contract and slow blood flow.
Endometrial polyps, which are small growths on the uterine lining itself, can also cause heavy or irregular bleeding. Unlike fibroids, polyps are usually soft and relatively small, but even a single polyp in the right location can significantly increase flow.
Adenomyosis is a less well-known condition where tissue that normally lines the uterus grows into the muscular wall instead. This causes the uterus to enlarge and makes periods heavier, often with intense cramping. It’s frequently misdiagnosed or overlooked, but it’s one of the more likely explanations when someone in their 30s or 40s notices their periods getting progressively worse.
Bleeding Disorders You Might Not Know You Have
Von Willebrand disease is an inherited condition that affects how well your blood clots, and it’s far more common in people with heavy periods than most realize. In the general population, fewer than 1 percent of women carry the diagnosis. Among women with confirmed heavy menstrual bleeding, the estimated prevalence jumps to somewhere between 5 and 20 percent.
Many people with von Willebrand disease go years without a diagnosis because heavy periods feel “normal” to them, especially if their mothers and sisters bled heavily too (since the condition is genetic). Other clues include easy bruising, prolonged bleeding after dental work or minor cuts, and significant bleeding after childbirth. If any of those ring true alongside heavy periods, a blood test can identify the disorder.
Thyroid Problems and Heavy Bleeding
An underactive thyroid (hypothyroidism) can make periods heavier through several overlapping mechanisms. Thyroid hormones and reproductive hormones are regulated by closely connected systems in the brain, and when thyroid function drops, it can disrupt the signals that control ovulation and the menstrual cycle. On top of that, hypothyroidism shifts the blood’s clotting balance toward a state where clots form less efficiently, which means more bleeding when the uterine lining sheds.
Other symptoms of hypothyroidism, like fatigue, weight gain, feeling cold, and dry skin, often accompany the heavier periods. A simple blood test can check thyroid function, and treating the thyroid problem frequently improves menstrual flow without any additional intervention.
Your IUD Could Be a Factor
If your periods got heavier after getting a copper (non-hormonal) IUD, the device is a very likely explanation. One study measuring blood loss before and after copper IUD insertion found that menstrual flow increased by an average of 55 percent at three months, jumping from about 59 mL to 91 mL per cycle. That increase tended to stay stable over the following nine months rather than improving.
Hormonal IUDs, by contrast, typically reduce menstrual bleeding substantially. If you have a copper IUD and the heavier flow is affecting your quality of life, switching to a hormonal option or a different contraceptive method is worth discussing.
How Heavy Periods Are Evaluated
Doctors classify heavy menstrual bleeding using a system called PALM-COEIN, which covers the major categories of causes: polyps, adenomyosis, fibroids (leiomyomas), malignancy or precancerous changes, clotting disorders (coagulopathy), ovulatory dysfunction, endometrial issues, medication-related (iatrogenic) causes, and a catch-all for anything else. The name is less important than what it represents: a structured checklist so nothing gets missed.
A standard workup starts with blood tests. A complete blood count reveals whether you’re anemic from chronic blood loss, and a ferritin level checks your iron stores, since ferritin drops well before your hemoglobin does. You’re considered iron-deficient at a ferritin level below 30 ng/mL, and anemic when hemoglobin falls below 12 g/dL. Thyroid function and, in some cases, clotting studies round out the initial bloodwork.
Imaging isn’t always the first step. Ultrasound is typically reserved for cases that don’t improve with initial treatment, or when fibroids, polyps, or adenomyosis are suspected based on symptoms or a physical exam. For younger patients, a transabdominal ultrasound (on the outside of the belly) is generally preferred over a transvaginal one.
The Iron Deficiency Connection
Chronic heavy periods are one of the leading causes of iron deficiency in premenopausal women, and this is the complication most likely to affect your daily life. Iron stores deplete gradually, so the symptoms sneak up: fatigue that doesn’t improve with sleep, difficulty concentrating, feeling winded during exercise you used to handle easily, headaches, and sometimes restless legs or cravings for ice or other non-food items.
Because the blood loss happens slowly over many cycles, your body partially adapts, and you may not realize how depleted you’ve become until the deficiency is significant. Ferritin testing is the most sensitive early indicator. If your ferritin is low, iron supplementation can start making a difference in energy levels within a few weeks, though it takes several months to fully rebuild stores. Treating the underlying cause of the heavy bleeding matters just as much, though, because supplementation alone can’t keep up with ongoing excessive loss indefinitely.