Abnormal Uterine Bleeding: What It Is, What Causes It, and When to Seek Medical Help
About one in three women seeks gynecological care at some point in their lives due to an episode of abnormal uterine bleeding. Although it is a common complaint in doctors’ offices, the topic is still shrouded in confusion: it is common for women to live for years with heavy, prolonged, or out-of-cycle bleeding without realizing that it warrants further investigation. The problem spans all phases of reproductive life and can arise during adolescence, adulthood, or the transition to menopause, with different causes and implications at each stage.
What makes this discussion more complex is the difficulty in distinguishing between what is a natural variation in the menstrual cycle and what is, in fact, a warning sign. Shorter or longer cycles, flow that varies from month to month, light spotting: all of these can be perfectly normal or may indicate conditions ranging from polyps and fibroids to endometriosis, polyendocrine metabolic ovarian syndrome (the new name for the former polycystic ovary syndrome), and hormonal changes associated with perimenopause. Without clear information, many women dismiss symptoms as normal when they could have been investigated sooner.
This guide summarizes what science and clinical practice say about abnormal uterine bleeding: what characterizes this condition, what the most common causes are depending on the stage of life, how to distinguish it from a simple menstrual irregularity, and, most importantly, when it’s worth seeking medical evaluation. The goal is to provide a reliable starting point for anyone who wants to better understand their own body and make more informed decisions about their health.
What is abnormal uterine bleeding, and how does it differ from an irregular period?
Abnormal uterine bleeding (AUB) is any bleeding that deviates from what is considered typical for a woman’s menstrual cycle. This can include very heavy or very prolonged periods, cycles with very short or very long intervals between them, or bleeding that occurs outside the expected menstrual period.
To understand what is considered abnormal, it’s helpful to know the reference parameters. A regular menstrual cycle typically ranges from 24 to 38 days. Menstrual bleeding lasts, on average, up to 8 days. Total blood loss per cycle ranges from 5 to 80 mL. In practice, the volume of bleeding is difficult to measure, but one must take into account the impact of the bleeding on the patient’s daily routine and, of course, signs and symptoms of systemic effects of the blood loss. When any of these parameters changes consistently, the condition can be classified as abnormal uterine bleeding.
The difference between a common irregular cycle and abnormal uterine bleeding lies largely in the persistence and intensity of the change. Having a shorter or longer cycle from time to time—especially during periods of stress or changes in routine—is relatively common. What warrants clinical attention is when these variations recur, intensify, or are accompanied by other symptoms, such as pelvic pain, severe fatigue, or the need to change sanitary pads very frequently.
What are the types of abnormal uterine bleeding?
The most current way to describe abnormal uterine bleeding, adopted by the International Federation of Gynecology and Obstetrics (FIGO), is based on four characteristics of the bleeding: frequency, regularity, duration, and volume. Older terms such as “menorrhagia” and “metrorrhagia” have been abandoned precisely because they cause confusion. Today, the main patterns are described as follows:
- Heavy menstrual bleeding: According to FIGO terminology, there is heavy menstrual bleeding (HMB), defined as an excessively heavy flow exceeding 80 mL per cycle, and heavy and prolonged menstrual bleeding (HPMB), which lasts 8 days or more. These terms have replaced the former term “menorrhagia.”.
- Intermenstrual bleeding: occurs between menstrual periods, outside the expected time frame. It replaces the term “metrorrhagia.”.
- Irregular bleeding: a variation of more than 20 days between cycles.
- Infrequent bleeding: cycles with intervals longer than 38 days.
- Frequent bleeding: cycles with intervals of less than 24 days—that is, periods that occur very close together.
- Postmenopausal bleeding: any vaginal bleeding that occurs after 12 consecutive months without a menstrual period.
These patterns help healthcare professionals describe the condition and guide the investigation, but they can overlap: a single woman may experience both heavy flow and bleeding between cycles at the same time. To categorize the causes of bleeding, FIGO also uses a second system, PALM-COEIN, which distinguishes between structural causes (such as polyps, fibroids, and adenomyosis) and nonstructural causes (such as coagulation disorders, ovulatory dysfunction, and hormonal changes).
Most Common Causes at Each Stage of a Woman's Life
The causes of abnormal uterine bleeding vary depending on age and hormonal status. Understanding this variation is important because the same symptom can have very different causes depending on a woman’s stage of life.
Adolescence and the Start of Reproductive Life
In the first few years after menarche (the first menstrual period), it is relatively common for cycles to be irregular. The hormonal system is still maturing, and anovulatory cycles—in which ovulation does not occur—can cause unpredictable bleeding. According to the American College of Obstetricians and Gynecologists (ACOG), it can take 6 years or more after the onset of menstruation for the cycle to become regular.
When bleeding is very heavy or persistent at this stage, it is worth investigating coagulation disorders, such as von Willebrand disease, which can manifest precisely as very heavy menstrual periods beginning in adolescence.
Adult reproductive age
In adulthood, the causes vary. Structural changes in the uterus, such as fibroids and endometrial polyps, are among the most common. Hormonal conditions, such as polyendocrine metabolic ovarian syndrome (PMOS)—recently renamed, though still widely known as polycystic ovary syndrome (PCOS)—can also cause irregular cycles and abnormal bleeding.
Endometriosis, although best known for causing pelvic pain, can contribute to changes in menstrual flow. Thyroid disorders, the use of certain contraceptive methods, and even chronic stress are factors that can influence bleeding patterns during this phase.
Pregnancy and its complications, such as threatened miscarriage or ectopic pregnancy, must also be considered whenever there is unexpected bleeding in women of childbearing age.
Perimenopause and Menopause
During the transition to menopause, hormonal fluctuations intensify. It is common for cycles to become shorter, then more spaced out, with variations in the volume of menstrual flow. This is part of the natural process of ovarian aging, but it warrants attention when bleeding becomes very heavy, very frequent, or occurs after a period without menstruation.
Any vaginal bleeding that occurs after 12 consecutive months without a menstrual period is considered postmenopausal bleeding and must be investigated. Although most cases have benign causes, such as endometrial atrophy, this type of bleeding may be associated with conditions that require careful evaluation, including endometrial hyperplasia.
Can abnormal uterine bleeding be related to endometriosis or SOMP (formerly known as SOP)?
Yes, and this situation is more common than many women realize.
Before we continue, a clarification about the name: in May 2026, an international consensus published in the journal *The Lancet* began referring to polycystic ovary syndrome as polyendocrine metabolic ovarian syndrome (PMOS). The change acknowledges that the condition extends beyond the ovaries and involves broader hormonal and metabolic changes. The diagnostic criteria and treatment remain the same; only the name has changed, and the transition will be gradual through 2028. Therefore, you will still see both acronyms—PCOS and MOMS—in use for a while.
Polyeendocrine metabolic ovarian syndrome (PMOS), formerly known as polycystic ovary syndrome, is one of the most common hormonal causes of abnormal uterine bleeding in women of reproductive age. According to the Cochrane Network, it may be associated with oligovulation or anovulation. In these cycles, the absence or irregularity of ovulation can lead to prolonged stimulation of the endometrium by estrogen, without adequate counterbalancing by progesterone. As a result, long cycles and irregular bleeding may occur, which can sometimes be heavy or unpredictable.
Endometriosis, in turn, can alter the menstrual cycle in various ways. In addition to the characteristic pelvic pain, some women with endometriosis experience heavier menstrual flow, bleeding between periods, or spotting (light bleeding) before their period. The exact mechanism varies depending on the location and extent of the endometriotic implants.
In both cases, abnormal bleeding is usually just one of the symptoms of a broader condition. Therefore, the clinical evaluation must take into account the patient’s overall symptoms and medical history, rather than focusing solely on the bleeding itself.
Signs that bleeding requires urgent medical evaluation
Not all abnormal bleeding requires an immediate trip to the emergency room, but some signs call for prompt attention. It’s important to seek urgent medical evaluation when the following occur (ACOG and Febrasgo):
● Heavy vaginal bleeding that soaks through a pad every hour for two or more consecutive hours.
● Bleeding accompanied by dizziness, fainting, paleness, or severe weakness, which may indicate complications resulting from blood loss.
● Vaginal bleeding during pregnancy, at any stage.
● Any bleeding after confirmed menopause (12 months without a period).
Even outside of these emergency situations, it is important to seek medical advice whenever there is a persistent change in your menstrual cycle. Periods that last much longer than usual, heavier flow for no apparent reason, or bleeding between periods that persists for more than two or three months are all sufficient reasons to see a gynecologist.
How the diagnosis is usually made
The evaluation of abnormal uterine bleeding begins with a clinical interview. The healthcare provider will want to understand the patient’s menstrual history: when her cycles began, what her previous pattern was, when she first noticed the change, whether there are any associated symptoms, and what medications or contraceptive methods she is currently using.
Based on that conversation, the most common tests performed during the evaluation include:
● Pelvic or transvaginal ultrasound: This allows for the evaluation of the uterus, ovaries, and endometrium, identifying fibroids, polyps, cysts, and changes in endometrial thickness.
● Blood tests: complete blood count to assess anemia, hormone levels (such as TSH, prolactin, FSH, and estradiol), pregnancy test, and, in some cases, coagulation tests.
● Hysteroscopy: a procedure that allows for direct visualization of the uterine cavity; it is indicated when polyps, submucosal fibroids, or other intracavitary abnormalities are suspected.
● Endometrial biopsy: the collection of a small sample of the endometrium for analysis; this procedure is particularly recommended for women over 45 or those with risk factors for endometrial hyperplasia.
The choice of tests depends on the patient’s age, her symptoms, and the initial clinical suspicion. Not every woman with abnormal bleeding will need all of these tests.
Is there a treatment for abnormal uterine bleeding?
Yes, and treatment depends directly on the identified cause, the patient's age, the severity of the symptoms, and each woman's reproductive plans.
Generally speaking, these approaches fall into two broad categories:
Clinical (pharmacological) treatment
This includes the use of hormonal medications, such as oral contraceptives, progestins, or hormonal intrauterine devices, which help regulate the cycle and reduce menstrual flow. Nonsteroidal anti-inflammatory drugs (NSAIDs) and antifibrinolytics, considered nonhormonal treatments, may also be prescribed to control the amount of bleeding. The choice of medication is individualized and should be made by a healthcare professional.
Surgical treatment
In cases of structural abnormalities, such as polyps or fibroids, surgical procedures may be necessary. Polypectomy and myomectomy are options aimed at removing the lesions while preserving the uterus. In more complex situations or when there is no desire to have children, endometrial ablation or hysterectomy may be considered.
The most important thing is for treatment to be based on a clear diagnosis. Treating bleeding without understanding its cause can mask conditions that require specific management. That is why a medical evaluation is always the first step.
Frequently Asked Questions About Abnormal Uterine Bleeding
Is bleeding outside of the menstrual period always a sign of illness?
Not necessarily. Light spotting can occur due to hormonal birth control, stress, ovulation, or normal variations in the menstrual cycle. However, if the bleeding recurs, is heavy, or is accompanied by pain, it is important to seek a gynecological evaluation to rule out causes that require treatment.
Is an irregular period the same thing as abnormal uterine bleeding?
Not exactly. Occasional variations in the menstrual cycle can be normal, especially during phases such as adolescence or perimenopause. Abnormal uterine bleeding is characterized by persistent or significant changes in the volume, duration, or interval between cycles, and generally warrants clinical evaluation.
Which doctor should you see if you have abnormal uterine bleeding?
According to ACOG, a gynecologist is the most appropriate professional to evaluate, investigate, and manage abnormal uterine bleeding. In emergency situations, such as very heavy bleeding accompanied by dizziness, a feeling of faintness, shortness of breath, chest pain, or a rapid pulse, you should also go to the emergency room.
Is bleeding after menopause normal?
No. Any vaginal bleeding that occurs after 12 consecutive months without a menstrual period should be investigated. Although many causes are benign, such as endometrial atrophy, postmenopausal bleeding may be associated with conditions that require careful evaluation. A medical consultation is essential.
Can abnormal uterine bleeding cause anemia?
Yes. Heavy or prolonged bleeding can lead to significant iron loss, resulting in iron-deficiency anemia. Symptoms such as excessive fatigue, paleness, shortness of breath, and dizziness may indicate that the bleeding is affecting hemoglobin levels. Medical follow-up allows for the identification and treatment of both the cause of the bleeding and the associated anemia.
Understanding your own menstrual cycle and noticing when something changes is a practical way to take care of your health. If any of the signs described here match your experience, the next step is to talk to a healthcare professional who can evaluate your situation on an individual basis.
Sources consulted