Uterine bleeding refers to any bleeding that originates from the uterus. While monthly menstrual periods are the most familiar form, the term usually comes up when bleeding falls outside the normal pattern. A normal menstrual cycle occurs every 24 to 38 days, lasts 2 to 7 days, and involves roughly 5 to 80 mL of blood loss. When bleeding deviates from any of those parameters, whether in timing, duration, heaviness, or regularity, it’s classified as abnormal uterine bleeding, or AUB.
What Counts as Abnormal
AUB is defined by four measurable dimensions: how often periods come, how regular they are, how long each one lasts, and how much blood you lose. A variation in any single dimension qualifies. That means periods arriving more often than every 24 days or less often than every 38 days, bleeding that stretches beyond 7 days, cycles that swing unpredictably in length, or flow heavy enough to soak through a pad or tampon every hour or two.
Estimated blood volumes above 100 mL per period are considered excessive. For perspective, a fully soaked regular pad holds about 5 mL, and a fully soaked super tampon holds roughly 10 mL. If you’re consistently changing protection every one to two hours, passing clots larger than a quarter, or bleeding through clothing or bedding, your flow likely falls well above normal range.
Structural Causes
Gynecologists categorize the causes of abnormal uterine bleeding using a system called PALM-COEIN. The first half, PALM, covers structural problems that can be seen on imaging or a tissue sample.
- Polyps: Small growths on the uterine lining. Most are benign, but they can cause spotting between periods or heavier flow.
- Adenomyosis: Tissue that normally lines the uterus grows into the muscular wall instead, often causing heavy, painful periods.
- Leiomyomas (fibroids): Noncancerous growths in or on the uterine wall. Their size and location determine whether they affect bleeding. Fibroids that push into the uterine cavity tend to cause the most trouble.
- Malignancy and hyperplasia: Precancerous thickening of the uterine lining, or uterine and cervical cancers. These are less common overall but become more important to rule out as you age.
Non-Structural Causes
The COEIN half of the system covers causes you can’t see on an ultrasound.
- Coagulopathy: Bleeding disorders that impair your blood’s ability to clot. About 20% of adolescents with heavy menstrual bleeding have an underlying clotting disorder.
- Ovulatory dysfunction: When the ovary doesn’t release an egg on a regular schedule, hormone signals become unbalanced and the uterine lining builds up unevenly. This is the single most common cause of abnormal bleeding in teenagers and is also frequent in the years leading up to menopause.
- Endometrial factors: Problems with the lining itself, such as inflammation or issues with how the lining repairs after a period, even when hormone levels are normal.
- Iatrogenic causes: Bleeding triggered by medications or devices. Hormonal contraceptives, blood thinners, and intrauterine devices can all change bleeding patterns.
- Not yet classified: A catch-all for rare or poorly understood causes that don’t fit neatly elsewhere.
How Causes Differ by Age
In adolescents, structural problems account for only about 1.3 to 1.7% of abnormal bleeding cases. The overwhelming cause is an immature hormonal feedback loop between the brain and ovaries, leading to cycles where ovulation doesn’t happen. Without ovulation, progesterone never rises to stabilize the uterine lining, so bleeding becomes irregular and sometimes very heavy.
In the 30s and 40s, structural causes become more prominent. Fibroids and polyps are increasingly common, and adenomyosis typically shows up in the late reproductive years. Ovulatory dysfunction returns as a major player during perimenopause, when hormone levels become erratic again. After menopause, any uterine bleeding at all is considered abnormal and warrants prompt evaluation because the risk of an underlying cancer rises significantly.
Postmenopausal Bleeding and Cancer Risk
Any bleeding that occurs after 12 consecutive months without a period deserves investigation. The average risk of endometrial cancer in someone with postmenopausal bleeding is about 11%, and when all gynecological cancers are counted together (including cervical cancer), over one in five people with postmenopausal bleeding will have a malignancy identified. That’s high enough that no episode of postmenopausal bleeding should be dismissed, even if it’s just light spotting.
How Abnormal Bleeding Is Evaluated
The starting point for most evaluations is a pregnancy test (for anyone of reproductive age), blood counts to check for anemia, and thyroid and hormone level checks. An ultrasound, typically performed with a vaginal probe, gives a view of the uterine wall and lining to look for fibroids, polyps, or unusual thickening.
If the ultrasound suggests something inside the uterine cavity, a sonohysterography (where a small amount of saline is infused into the uterus during the ultrasound) provides a clearer picture. Hysteroscopy, a thin camera placed through the cervix, offers direct visualization and the ability to biopsy or remove abnormalities at the same time.
An endometrial biopsy is recommended for anyone over 45 with abnormal bleeding, and for younger individuals who have risk factors for uterine lining overgrowth, such as polycystic ovary syndrome, obesity, or bleeding that hasn’t responded to treatment. One important caveat: a biopsy can miss a cancer if it occupies less than half the surface of the uterine cavity, so persistent bleeding after a negative biopsy still warrants further investigation.
Treatment Options
Treatment depends on the cause, the severity of bleeding, and whether you want to preserve fertility. For non-structural causes, hormonal therapies are the usual first line. A hormonal intrauterine device that releases a small amount of progestin directly into the uterus is one of the most effective options, reducing menstrual blood loss substantially while also providing contraception. Combined hormonal contraceptives (pills, patches, or rings) regulate cycles by supplying steady hormone levels. For people who prefer non-hormonal options, anti-inflammatory medications taken during the period can reduce flow by about 20 to 50%, and a medication that helps blood clot more effectively at the uterine lining can cut blood loss by roughly half.
When medical treatment fails or isn’t an option, surgical procedures come into play. Endometrial ablation destroys the uterine lining using heat, cold, or other energy sources. It significantly reduces or even stops menstrual bleeding and is appropriate for people with benign causes who don’t plan future pregnancies. Recovery is faster and less invasive than a hysterectomy. A hysterectomy, the complete removal of the uterus, is considered the definitive solution because it eliminates bleeding permanently, but it involves longer recovery and higher overall health care costs. It’s generally reserved for cases where other treatments haven’t worked, when cancer is found, or when someone has completed childbearing and wants a permanent resolution.
Anemia and Quality of Life
Heavy uterine bleeding doesn’t just stain clothing. It drains iron stores. Roughly two-thirds of people with heavy menstrual bleeding are anemic, a rate far higher than the general population. Iron deficiency anemia causes fatigue, weakness, difficulty concentrating, dizziness, and shortness of breath during everyday activities. Many people with heavy periods assume their tiredness is normal and live with it for years before anyone connects the dots to blood loss. If your periods are heavy and you’re constantly exhausted, a simple blood count can confirm whether anemia is part of the picture, and iron supplementation or treating the underlying bleeding can make a dramatic difference in energy levels.