A heavy period has several possible causes, ranging from a temporary hormonal shift to structural changes in the uterus. Clinically, a period is considered heavy when you lose more than 80 milliliters of blood per cycle, roughly the equivalent of soaking through a pad or tampon every hour for several consecutive hours. But you don’t need to measure your blood loss to know something feels off. If your period is disrupting your daily life, lasting longer than seven days, or producing clots the size of a quarter or larger, your flow qualifies as genuinely heavy.
Hormones That Control How Much You Bleed
The thickness of your uterine lining determines how much tissue and blood you shed each month, and that thickness is controlled by two hormones: estrogen and progesterone. During the first half of your cycle, estrogen builds the lining up. After ovulation, progesterone steps in to stabilize it and eventually trigger a controlled shed.
Problems start when that balance tips. If you don’t ovulate in a given cycle, your body never produces the progesterone needed to keep the lining in check. Estrogen continues thickening it unopposed, sometimes for weeks. When the lining finally sheds, there’s simply more of it, which means a heavier, longer period. This is one of the most common reasons for heavy flow, especially during the teen years when cycles are still maturing and during the years leading up to menopause when ovulation becomes irregular.
Sustained estrogen without progesterone can also cause the uterine lining to overgrow beyond what’s normal, a condition called endometrial hyperplasia. Left untreated over time, that overgrowth can become precancerous, which is one reason persistently heavy periods are worth investigating rather than just tolerating.
Fibroids, Polyps, and Other Structural Causes
Uterine fibroids are noncancerous growths in the muscular wall of the uterus, and they’re extremely common. They contribute to heavy bleeding through two mechanisms. First, fibroids expand the total surface area of the uterine lining, so there’s more tissue to shed. Second, they stiffen the uterine wall and disrupt the contractions your uterus normally uses to squeeze blood vessels shut and limit bleeding. When those contractions can’t work properly, bleeding is both heavier and more prolonged.
Fibroids that grow into or near the uterine cavity tend to cause the most noticeable bleeding changes. Smaller fibroids embedded deep in the muscle may cause no symptoms at all. The location matters more than the size.
Polyps, which are smaller growths on the lining itself, can also cause heavy or irregular bleeding. They’re softer than fibroids and typically easier to remove, but they can be just as disruptive to your cycle. Both fibroids and polyps are identified through imaging, most often an ultrasound.
Adenomyosis: A Frequently Missed Cause
Adenomyosis occurs when tissue that normally lines the uterus grows into the muscular wall itself. This makes the uterus enlarged, boggy, and prone to heavy, painful periods. It’s often confused with fibroids because the symptoms overlap, and for years it could only be confirmed after a hysterectomy. Improved imaging has made it easier to diagnose while you’re still weighing your options.
Adenomyosis is most common in your 30s and 40s, though it can occur earlier. If your heavy flow comes with intense cramping and your uterus feels tender during an exam, this is one possibility your doctor may explore.
Bleeding Disorders You May Not Know About
Between 5% and 24% of women with chronic heavy periods turn out to have an underlying bleeding disorder. The most common is von Willebrand disease, a condition where your blood doesn’t clot efficiently. Many women with this condition go undiagnosed for years because heavy periods are often dismissed as normal or attributed to hormones alone.
Clues that a bleeding disorder might be involved include heavy periods that started with your very first cycle, a history of easy bruising, prolonged bleeding after dental work or surgery, or a family member with similar symptoms. If your heavy flow has never responded well to typical hormonal treatments, a bleeding disorder is worth ruling out with a simple blood test.
Copper IUDs and Medications
If your heavy flow started after getting a copper IUD, that’s likely the direct cause. Studies show menstrual blood loss increases by about 50 to 55% with a copper IUD, jumping from roughly 59 mL to 91 mL per cycle on average. This increase typically shows up within the first three months and stays relatively stable from there. For many people this is tolerable, but if you were already on the heavier side, it can push you into territory that feels unmanageable.
Blood thinners and certain anti-inflammatory medications can also increase menstrual bleeding. If your flow changed noticeably after starting a new medication, that connection is worth mentioning to your provider.
When Heavy Flow Leads to Iron Deficiency
The biggest day-to-day consequence of heavy periods is iron loss. Every cycle drains iron from your body, and if your flow is heavy enough, you can’t replenish it through diet alone. Iron deficiency develops gradually. Long before your blood counts drop into anemia territory, low iron stores cause fatigue, brain fog, headaches, restless legs, and exercise intolerance that you might chalk up to stress or poor sleep.
Iron deficiency is typically diagnosed when ferritin, the protein that stores iron in your body, drops below 30 micrograms per liter. But symptoms can begin at levels below 50, which is why some guidelines now recommend treatment at that threshold. Iron deficiency anemia, the more advanced stage, is defined by a hemoglobin level below 120 grams per liter in women. If you’ve had heavy periods for months or years and feel perpetually drained, a ferritin test is more revealing than a standard blood count alone, since hemoglobin can remain normal even when your iron stores are depleted.
How Heavy Bleeding Is Evaluated
The first step is usually a transvaginal ultrasound. It’s noninvasive, painless, and good at picking up fibroids, polyps, and abnormal lining thickness. It’s often enough to identify or rule out the most common structural causes.
If the ultrasound is inconclusive or your doctor suspects endometrial hyperplasia, a hysteroscopy offers a more detailed look. This involves passing a thin camera through the cervix to directly visualize the uterine cavity. It’s more accurate than ultrasound for detecting lining abnormalities and allows your doctor to biopsy suspicious areas or remove polyps during the same procedure.
Blood work typically includes a complete blood count to check for anemia, iron studies including ferritin, and thyroid function. Depending on your history, your provider may also screen for bleeding disorders or check hormone levels. Most of this workup can happen in a single office visit.
Signs Your Flow Needs Attention
Not every heavy period signals a problem. A single unusually heavy cycle can happen after a stressful month, a missed ovulation, or an early miscarriage you may not have known about. But certain patterns point to something that won’t resolve on its own:
- Soaking through a pad or tampon every hour for two or more consecutive hours
- Clots the size of a quarter or larger
- Periods lasting longer than seven days
- Needing to change protection overnight regularly
- Fatigue, dizziness, or shortness of breath that worsens around your period
These symptoms don’t always mean something serious is wrong, but they do mean your body is losing more blood than it can comfortably replace. Identifying the cause usually leads to straightforward treatment, whether that’s hormonal, procedural, or as simple as correcting an iron deficit you didn’t know you had.