Abnormal uterine bleeding (AUB) is any bleeding from the uterus, outside of pregnancy, that differs from a normal menstrual period in its timing, frequency, heaviness, or duration. It affects up to one-third of women at some point during their reproductive years, with the highest rates occurring in teenagers who have just started menstruating and in women approaching menopause. When irregular and between-period bleeding are included alongside heavy periods, prevalence estimates reach 35% or higher.
What Counts as Abnormal
A typical menstrual cycle lasts 24 to 38 days, with bleeding that runs 4 to 8 days. Anything that falls outside those ranges can qualify as abnormal. That includes periods arriving unpredictably, lasting longer than 8 days, cycles shorter than 24 days or longer than 38 days, bleeding between periods, and bleeding after sex.
Heavy menstrual bleeding gets the most attention. Clinically, it has been defined as losing more than 80 milliliters of blood per cycle, but that number isn’t especially useful in real life since no one measures their blood loss in a lab. A more practical gauge: if you’re regularly soaking through a pad or tampon every hour or two, passing clots larger than a quarter, or needing to double up on protection, your flow is heavier than normal.
Structural Causes
Doctors classify AUB causes using a system called PALM-COEIN, which separates structural problems (things that can be seen on imaging or under a microscope) from non-structural ones. The structural category includes four main culprits.
- Polyps: Small, usually noncancerous growths on the uterine lining that can cause spotting between periods or heavier-than-normal flow.
- Adenomyosis: A condition where tissue that normally lines the uterus grows into the muscular wall, often causing heavy, painful periods and a feeling of pelvic pressure.
- Leiomyomas (fibroids): Benign muscle tumors in or on the uterus. Fibroids that press into the uterine cavity are the ones most likely to cause heavy or prolonged bleeding.
- Malignancy and hyperplasia: Uterine cancer or precancerous overgrowth of the lining. This is less common, especially in younger women, but it’s the reason persistent abnormal bleeding always warrants evaluation.
Non-Structural Causes
The non-structural side of the classification covers problems that won’t show up on an ultrasound.
Ovulatory dysfunction is one of the most common explanations, particularly in teens and in the years leading up to menopause. When the ovary doesn’t release an egg, the body doesn’t produce progesterone to stabilize the uterine lining. Without that hormonal signal, the lining keeps thickening under the influence of estrogen alone. Eventually it outgrows its blood supply, becomes unstable, and sheds irregularly and heavily. The blood vessels in an estrogen-only lining are also more fragile, which adds to the volume of bleeding.
Coagulopathy refers to bleeding disorders. Conditions like von Willebrand disease can make it harder for blood to clot normally, leading to heavy periods that start in adolescence and persist. This cause is underdiagnosed: many women with a clotting disorder assume their heavy periods are just “how they are.”
Other non-structural categories include problems with the endometrial lining itself (where inflammation or changes in local clotting factors cause abnormal shedding) and iatrogenic causes, meaning bleeding triggered by medications or devices. Hormonal contraceptives, blood thinners, and even copper IUDs can all alter bleeding patterns.
How AUB Is Diagnosed
The workup typically starts with a detailed history of your bleeding pattern: how often your periods come, how long they last, how heavy they are, and whether you bleed between cycles. Keeping a record for two or three cycles before your appointment helps. A complete blood count checks for anemia, which is common in women with heavy or prolonged bleeding, and may reveal signs of infection. Thyroid function and hormone levels are often checked as well, since thyroid problems and conditions like polycystic ovary syndrome can both disrupt cycles.
Imaging usually means a pelvic or transvaginal ultrasound to look for structural issues like fibroids, polyps, or thickened uterine lining. If the ultrasound raises questions, a saline infusion sonogram (where a small amount of fluid is placed in the uterus to improve the ultrasound view) can give a clearer picture. An endometrial biopsy, a quick in-office procedure that samples the uterine lining, is recommended when there’s a concern about hyperplasia or cancer, especially for women over 45 or those with risk factors like obesity or prolonged irregular bleeding.
Treatment Options
Treatment depends on the cause, your age, how severe the bleeding is, and whether you want to become pregnant in the future. For many women, medication is the first step.
Hormonal approaches are the most widely used. A hormonal IUD that releases a small amount of progestin directly into the uterus is one of the most effective options, significantly reducing menstrual blood loss while also providing contraception. Birth control pills, progestin-only pills, and injectable progestins can regulate cycles and thin the uterine lining. For women who can’t or prefer not to use hormones, a medication called tranexamic acid helps blood clot more effectively at the uterine lining and can reduce blood loss by roughly 50%. Anti-inflammatory medications taken during your period can also reduce flow and cramping.
The challenge with daily medications is consistency. Many women find that the inconvenience of taking pills every day, especially when side effects crop up, leads them to stop treatment before it has a chance to work. A hormonal IUD sidesteps that issue since it works continuously for several years once placed.
When Procedures Are Needed
If medications don’t provide enough relief, or if the bleeding has a structural cause that won’t respond to hormones, procedural options include endometrial ablation (which destroys the uterine lining to reduce or stop bleeding), removal of polyps or fibroids through a scope inserted into the uterus, uterine artery embolization (which cuts off blood flow to fibroids and shrinks them without surgery), and hysterectomy as a definitive solution. Uterine artery embolization is a good option for women who want to keep their uterus but haven’t found relief with medication. Hysterectomy permanently ends menstruation and is typically reserved for cases where other treatments have failed or cancer is present.
Signs That Need Urgent Attention
Most abnormal bleeding is not an emergency, but some situations require immediate care. If you’re soaking through a pad or tampon every hour for more than two hours straight and also experiencing chest pain, shortness of breath, or dizziness, that combination signals dangerous blood loss. Severe fatigue, pale skin, and a racing heartbeat at rest are signs of significant anemia that has developed over time and also need prompt evaluation. Postmenopausal bleeding (any bleeding after your periods have stopped for 12 months) is always worth reporting to your doctor promptly, as it can be an early sign of uterine cancer.