A normal period lasts about four to five days, with total blood loss of roughly two to three tablespoons. Periods lasting more than seven days are considered prolonged, and they often come with heavier flow as well. The causes range from common hormonal shifts to structural changes in the uterus, and identifying the right one matters because the treatment is very different depending on what’s behind it.
Hormonal Imbalances and Missed Ovulation
Your menstrual cycle depends on a carefully timed rise and fall of estrogen and progesterone. Estrogen thickens the uterine lining in the first half of your cycle, and progesterone stabilizes it after ovulation. When you don’t ovulate, progesterone never shows up to do its job. The lining keeps growing under estrogen’s influence, becoming thicker and more fragile. When it finally sheds, the bleeding is heavier and takes longer to stop.
This pattern of skipped ovulation is common in polycystic ovary syndrome (PCOS), one of the most frequent causes of irregular, prolonged periods in younger women. It also happens during times of significant stress, rapid weight changes, or intense exercise. Chronic anovulation isn’t just inconvenient. Over time, the constant estrogen exposure without progesterone to balance it raises the risk of abnormal thickening of the uterine lining.
Fibroids and Adenomyosis
Uterine fibroids are noncancerous growths in the muscular wall of the uterus. They cause longer, heavier periods through several mechanisms at once: they increase the overall surface area of the uterine lining, boost blood flow into the uterus, and interfere with the uterus’s ability to contract and squeeze blood vessels shut after shedding. Fibroids that bulge into the uterine cavity (submucosal fibroids) are the worst offenders because they can ulcerate the lining directly above them, creating an additional source of bleeding.
Adenomyosis is a related condition where tissue that normally lines the inside of the uterus grows into the muscular wall instead. Like fibroids, it disrupts the uterus’s ability to contract effectively. It also compresses the overlying lining, and the proportion of glandular tissue embedded in the muscle wall correlates with how heavy the bleeding gets. Adenomyosis is especially common in women in their 30s and 40s and often coexists with fibroids, compounding the problem.
Thyroid Problems
An underactive thyroid can make periods longer and heavier in a way that surprises many people: it changes how your blood clots. Low thyroid hormone levels shift the body’s clotting system toward thinner, more easily dissolved clots. Specifically, the body produces less of a key clotting protein called von Willebrand factor, and levels of several other clotting factors drop as well. Platelet function also becomes less effective.
The result is that when you bleed during your period, the normal clotting mechanisms that help stop the flow don’t work as efficiently. This effect reverses when thyroid hormone levels are corrected, which is one reason thyroid testing is a standard part of evaluating unexplained heavy or prolonged periods.
Bleeding Disorders
Some women have had long, heavy periods since their very first cycle and assume it’s just how their body works. In a significant number of these cases, a bleeding disorder is the underlying cause. Von Willebrand disease, the most common inherited bleeding disorder, is found in an estimated 5% to 20% of women with unexplained heavy menstrual bleeding. That’s a remarkably high rate for a condition many people have never heard of.
Clues that a bleeding disorder might be involved include heavy periods that started at puberty and never improved, a tendency to bruise easily, prolonged bleeding after dental work or minor cuts, or a family history of bleeding problems. Basic screening involves blood tests that check clotting time and platelet counts.
Perimenopause
The transition to menopause typically begins in your 40s, though it can start earlier. During perimenopause, estrogen and progesterone levels rise and fall unpredictably rather than following their usual monthly rhythm. Ovulation becomes erratic, so some cycles produce plenty of progesterone and others produce almost none. The cycles without ovulation lead to the same problem described above: an overgrown, unstable lining that bleeds heavily and for longer.
You might have a perfectly normal period one month, skip the next, then have one that drags on for 10 days with heavy flow. This variability is the hallmark of perimenopause. The time between periods can also shift, getting shorter or longer without warning. These changes can continue for several years before periods stop entirely.
Copper IUD
If your periods became longer after getting a copper IUD, the device itself is the likely cause. Copper IUDs are well known for increasing both the duration and heaviness of menstrual bleeding. This is one of the most common side effects and the primary reason some women have the device removed. The good news is that for many people, the increase in bleeding eases up after three to six months as the uterus adjusts.
Polyps and Other Structural Causes
Endometrial polyps are small, soft growths on the uterine lining. They’re usually benign but can cause bleeding between periods, longer periods, or spotting after menopause. Unlike fibroids, which grow in the muscle, polyps grow directly on the surface where bleeding occurs. They’re typically identified through ultrasound and can be removed in a straightforward procedure.
How Prolonged Periods Affect Your Health
The most immediate consequence of long or heavy periods is iron deficiency. Your body loses iron with every milliliter of blood, and when periods consistently last more than seven days or involve heavy flow, iron stores deplete faster than diet alone can replace them. About 30% of women with heavy menstrual bleeding have iron deficiency (defined as a ferritin level at or below 15 ng/mL), and 60% have progressed to full iron-deficiency anemia.
Iron-deficiency anemia causes fatigue, weakness, difficulty concentrating, shortness of breath during activities that used to feel easy, and sometimes dizziness or headaches. Many women with gradually worsening periods adapt to these symptoms without realizing how much their energy and quality of life have declined. A simple blood test checking hemoglobin (anemia is defined as below 12 g/dL in non-pregnant women) and ferritin levels can reveal whether your periods have been quietly draining your iron reserves.
What to Expect During Evaluation
If you’re being evaluated for prolonged periods, the workup typically starts with a pregnancy test (regardless of how unlikely you think it is) and a complete blood count to check for anemia. From there, the tests depend on what your doctor suspects. Thyroid function is checked when there’s no obvious cause or when you have other symptoms like fatigue, weight changes, or cold sensitivity. Hormone levels are tested when conditions like PCOS seem likely. Clotting studies screen for bleeding disorders.
Imaging usually involves a transvaginal ultrasound, which is the best first-line tool for spotting fibroids, polyps, and adenomyosis. If the ultrasound findings are unclear or your doctor needs a closer look at the uterine lining, an endometrial biopsy may be recommended. This involves taking a small tissue sample from the lining, primarily to rule out abnormal cell growth, especially in women over 40 or those with risk factors like prolonged anovulation or obesity.
Tracking your periods before your appointment helps enormously. Note how many days you bleed, how often you change a pad or tampon (and how saturated it is), whether you pass clots, and how many days fall between cycles. This information gives your provider a much clearer picture than a vague description of “heavy” or “long” periods.