INTRODUCTION — Conflicting terminology to describe abnormal uterine bleeding (AUB) dates back to the late 1700s [1] and has led to difficulties in many areas, including documenting symptoms; reaching consensus on the use of diagnostic techniques and medical and surgical therapies; designing and interpreting basic, translational, and clinical research; and conducting multicenter or multinational clinical trials [2-5]. These concerns led to the formation of the Menstrual Disorders Working Group within the International Federation of Gynecology and Obstetrics (FIGO), which has subsequently become the Menstrual Disorders Committee (MDC), a standing FIGO committee.

The initial developmental process in 2005 started using a modified Delphi method [6] involving a spectrum of stakeholders from gynecologic societies, journals, regulatory bodies, epidemiologists, and basic, translational, and clinical scientists. One goal was to create a clearly defined system for AUB terminology written in English that could be easily translated into other languages and readily understood by clinicians, patients, and researchers [2,3]. Where possible, the definitions were based on data derived from population-based studies. The classification system was conceived to allow the clinician, educator, or researcher to consider all possible causes or contributors to AUB in a given patient, understanding that some imaged lesions may be asymptomatic. There has been an ongoing structured process of evaluation and, where necessary, modification of the systems.

Since 2005, the FIGO MDC has developed internationally supported recommendations for:

●Definitions of, and terminology for, normal menstrual bleeding and AUB symptoms [2,3,7]: FIGO AUB System 1 for nomenclature and definitions of normal and AUB [8,9].

●A classification of underlying causes of AUB in the reproductive years unrelated to pregnancy [7]: FIGO System 2, also known as the PALM-COEIN System (Polyp, Adenomyosis, Leiomyoma, Malignancy and hyperplasia, Coagulopathy, Ovulatory dysfunction, Endometrial dysfunction, Iatrogenic, and "Not otherwise classified") categorization of causes of AUB [8,9].

Together, these terminology and classification systems provide the tools to improve precision in communicating about etiologies, symptoms, diagnosis, and treatment of AUB in nonpregnant reproductive-aged females.

Both FIGO AUB Systems 1 and 2, the latter also known as the PALM-COEIN System, are discussed here. The differential diagnosis, approach to the evaluation of AUB, and management of AUB in nonpregnant reproductive-aged females are reviewed in detail separately. (See "Abnormal uterine bleeding in nonpregnant reproductive-age patients: Evaluation and approach to diagnosis" and "Differential diagnosis of genital tract bleeding in women" and "Abnormal uterine bleeding: Management in premenopausal patients".)

Premenarchal bleeding, postmenopausal bleeding, and pregnancy-related bleeding are also discussed separately. (See "Evaluation of vulvovaginal bleeding in children and adolescents" and "Approach to the patient with postmenopausal uterine bleeding" and "Overview of the etiology and evaluation of vaginal bleeding in pregnancy".)

FIGO AUB SYSTEM 1: NOMENCLATURE AND DEFINITIONS OF NORMAL AND ABNORMAL UTERINE BLEEDING

Definition of normal uterine bleeding (menstruation) — The four parameters used to define normal uterine bleeding are frequency, regularity, duration, and volume (table 1 and figure 1) [2,3]. Assessment is generally based upon the patient's experience in the previous six months. The four parameters apply to patients who are not taking local or systemic gonadal steroids or other drugs that might directly impact gonadal steroid production or endometrial function. Such agents frequently have an impact on uterine bleeding and may include progestin-based contraceptives with or without estrogen, gonadotropin-releasing hormone agonists or antagonists, aromatase inhibitors, and selective estrogen or progesterone receptor modulators.

●Frequency – Normal frequency is onset of menstrual bleeding every 24 to 38 days.

●Regularity – When assessing regularity, cycle length is defined as the number of days from the start (day 1) of one period until the start (day 1) of the next period. Variation in cycle length (ie, the difference between the shortest to longest cycle) depends on age and is normal (regular) when (table 2) [8-10]:

•For ages 18 to 25 years: cycle variation ≤9 days

•For ages 26 to 41 years: cycle variation ≤7 days

•For ages 42 to 45 years: cycle variation ≤9 days

For age <18 and >45 years, the frequency of infrequent or unpredictable ovulation is much higher, rendering the definition of normal regularity in this population difficult.

●Duration – The normal number of bleeding days in a single menstrual period is ≤8 days [10-13].

There is no lower limit because a review of data found no specific pathologic entities associated with short periods and did not enable consensus regarding the lower limit of normal for the duration of menses.

●Volume – Normal volume is subjective and defined as menstrual blood loss volume that does not interfere with a patient's physical, social, emotional, and/or material quality of life [14,15].

For research that involves quantitative analysis of menstrual blood loss volume (including clots), the definition of normal is ≤80 mL menstrual blood loss per cycle.

The four parameters were based upon published population data and used medians and confidence intervals [2,3,8,9]. There were some variations within normal populations in the regularity and frequency of menstrual bleeding when the 5^th to 95^th percentiles were utilized, likely related to patients with ovulatory dysfunction in the normal population. For example, using these percentiles, the range of shortest to longest cycle in population studies was 2 to 20 days [2,3,11]; however, when it was determined that many patients have a single short or long cycle each year, the definition was revised to utilize the 75^th percentile to define the normal range [8-10]. Little is known about cultural, ethnic, or geographic variations since comparative large-scale studies have not been conducted [2,3].

Definition of AUB — AUB is defined as any variation in frequency, regularity, duration, or volume from normal uterine bleeding (see 'Definition of normal uterine bleeding (menstruation)' above) and also includes intermenstrual bleeding (IMB) and unscheduled bleeding when using progestin±estrogen gonadal steroids of various types and with varying delivery routes (algorithm 1 and table 1) [8,9].

AUB can be acute or chronic [7]:

●Acute AUB is an episode of bleeding from the uterine corpus of sufficient quantity to require immediate intervention to prevent further blood loss.

●Chronic AUB is bleeding from the uterine corpus that is abnormal in frequency, regularity, duration, and/or volume and has been present for at least the majority of the past six months.

The following terminology is used to describe abnormalities in menstrual frequency, regularity, duration, and volume, and IMB [10,11,13,16,17]. When asking patients about menstrual abnormalities, the clinician should consider symptoms experienced over at least the previous six months.

Abnormalities in frequency — (table 1 and figure 1)

●Frequent – Frequent menstrual bleeding refers to periods that start more often than every 24 days.

●Infrequent – Infrequent menstrual bleeding refers to periods that start less often than every 38 days. The older term for this symptom was "oligomenorrhea."

●Absent (primary and secondary amenorrhea)

•Primary amenorrhea is defined as the absence of menarche by age 15 years.

•Secondary amenorrhea is defined as absence of spontaneous menstrual bleeding for six months in a patient who previously had menstrual bleeding [18]. The duration of the period of amenorrhea should be specified.

It is important to note that some experts would prefer to add a caveat that "secondary amenorrhea is the absence of menses for more than three months in patients who previously had regular menstrual cycles or six months in patients who previously had irregular menses." The FIGO MDC did not make this part of their definition as it would lead to a large number of young patients with generally regular and normal menses being classified as "abnormal."

Abnormalities in regularity — (table 1 and figure 2)

●Irregular

•For ages 18 to 25: cycle length variance >9 days

•For ages 26 to 41: cycle length variance >7 days

•For ages 42 to 45: cycle length variance >9 days

For ages <18 or >45, the >9-day definition is also applied, although the evidence defining normal is somewhat less clear in these groups. For some adolescent patients who have occasional or frequent irregular and/or long cycles, typically, but not always, the cycle length evolves spontaneously to fit norms. For others, such an evolution may not occur.

Abnormalities in duration — (table 1 and figure 3)

●Prolonged menstrual bleeding is defined as menstrual periods consistently lasting >8 days. This phenomenon is often, but not always, associated with heavy menstrual bleeding (HMB) (see 'Abnormalities in volume' below).

Since there is no consensus on the lower limit of normal for the duration of menses, there is no abnormality termed "shortened menstrual bleeding."

Abnormalities in volume — (table 1 and figure 4)

●Heavy – For clinical purposes, HMB is defined as a volume that interferes with the patient's physical, social, emotional, and/or material quality of life [8,14,19]. It is based on the patient's perception of increased daily or total monthly volume of menstrual blood flow, regardless of the duration, the frequency, or whether the timing of onset is regular or irregular. Typically, HMB is part of a symptom complex that may include variable degrees of dysmenorrhea, fatigue, and other symptoms. It should be noted that some patients have had HMB "normalized" by parents or health care providers, so the clinician should take this into account.

For research purposes, the volumetric definition of HMB is >80 mL menstrual "blood" loss per cycle, a process that requires individuals to collect all menstrual products and other blood loss and submit them for laboratory analysis, usually via the alkaline hematin method, which is cumbersome and expensive [12,16,20]. Surrogate measures of menstrual volume are being developed; the most common are semiquantitative pictorial blood loss assessment charts [21,22].

●Light – Light menstrual bleeding is also defined by the individual. It is uncommon and rarely related to pathology, although it may be a presenting symptom of cervical stenosis or intrauterine synechiae. Individuals who express concern about light periods may perceive a heavy, red bleed as a sign of good health [23].

For research purposes, <5 mL is considered "low volume," a metric that can only be assessed quantitatively with methods like the alkaline hematin assay [16,24].

Intermenstrual bleeding — IMB refers to AUB that occurs between well-defined cyclical menses (figure 5).

IMB may be cyclical, with predictable bleeding occurring in the follicular (early) phase, midcycle, or luteal (late) phase of the cycle, depending on the endocrinologic basis for the symptom.

●Cyclical midcycle IMB – A small amount of clinically detectable vaginal bleeding arising from the endometrium around midcycle is common, occurring in approximately 9 percent of healthy reproductive-age patients [25]. This is thought to be associated with the midcycle drop in circulating estradiol levels that occurs just after ovulation [26].

●Cyclical premenstrual IMB – Cyclical IMB that predictably occurs late in the cycle (luteal phase) may be indicative of a luteal phase defect (poor corpus luteal development resulting in inadequate progesterone secretion and, in turn, inadequate development of the secretory endometrium).

IMB can also be unpredictable or related to contact.

●Acyclical IMB – IMB that is not cyclical or predictable is called random or acyclical IMB. Such bleeding is typically associated with nonmalignant lesions, such as chronic cervicitis or polyps of the cervix or endometrium, and postcoital bleeding is a frequent symptom. Although the uterine cavity (endometrium or cervical canal) is often not the source of acyclical IMB, it is associated with cervical or endometrial cancer in some cases.

Careful examination of the vagina and ectocervix is important before assuming that AUB is arising from the endometrium or ectocervix. Bleeding from focal lesions of the vagina or ectocervical os is generally acyclical and may be serious, such as cervical cancer. IMB can also be difficult to distinguish from irregular and/or very frequent menses, thus, care must be taken before applying the term IMB to patients with these other abnormalities. (See "Differential diagnosis of genital tract bleeding in women".).

Definitions for patients on hormonal medications — The descriptions of menstrual frequency, regularity, duration, and volume and IMB do not apply to patients who are taking local or systemic gonadal steroids or other drugs that might directly impact gonadal steroid production or endometrial function and, in turn, uterine bleeding. Examples include progestin-based contraceptives with or without estrogen, gonadotropin-releasing hormone agonists or antagonists, aromatase inhibitors, and selective estrogen or progesterone receptor modulators. Cyclically used hormonal methods typically lighten the flow (and often greatly) while those used continuously frequently result in unpredictable light bleeding or amenorrhea. The least predictable patterns tend to come with use of long-acting progestin-only contraceptives [27], and distinguishing between bleeding and spotting with these agents has been poorly defined. AUB in patients on hormonal contraception is discussed below. (See 'Iatrogenic causes (AUB-I)' below.)

It is important to have a standardized approach to describing AUB in patients using hormonal medications. The FIGO MDC used the 90-day reference period (duration of observation for analysis of bleeding episodes) and terminology for bleeding symptoms promoted by the World Health Organization (WHO) and others for vaginal bleeding patterns induced by fertility-regulating methods [13,28-31]. This terminology allows for several different analyses within each reference period (eg, number of patients using a specific medication and experiencing no, prolonged, frequent, infrequent, or irregular bleeding), which offers a useful degree of discrimination between different types of fertility-regulating therapy.

For individual patients, the number of bleeding and spotting days during the reference period is based on their diary. The distinction between bleeding and spotting is based on the patient's need for menstrual product use (table 3).

Terms that should be abandoned — There is consensus that some traditional AUB terms should be abandoned because they are confusing and/or poorly defined [2,3,5]. These terms include menorrhagia, metrorrhagia, polymenorrhea, hypermenorrhea, oligomenorrhea, and dysfunctional uterine bleeding.

FIGO AUB SYSTEM 2: PALM-COEIN CLASSIFICATION OF POTENTIAL CAUSES OF AUB IN THE REPRODUCTIVE YEARS

Overview — FIGO System 2, also known as the PALM-COEIN system, stratifies possible causes of AUB into nine basic categories, which are arranged according to the acronym PALM-COEIN: Polyp, Adenomyosis, Leiomyoma (Submucous or Other), Malignancy and hyperplasia, Coagulopathy, Ovulatory dysfunction, Endometrial dysfunction, Iatrogenic, and "Not otherwise classified." In general, the components of the PALM group are discrete ("structural") entities that are measurable visually using imaging techniques and/or with histopathology, whereas the COEIN group comprises entities that are generally not defined by imaging or histopathology ("nonstructural"). These entities can be organized in the form of a "matrix" to facilitate documentation of clinical evaluation and results (table 4).

The system was constructed recognizing that any nonpregnant reproductive-aged female could have one or multiple entities that could cause or contribute to AUB and that definable entities, such as adenomyosis, leiomyomas, and endocervical or endometrial polyps, may frequently be asymptomatic and therefore not necessarily a contributor to the presenting symptoms.

Under FIGO System 2/PALM-COEIN, diagnoses frequently encompassed within the previous term "dysfunctional uterine bleeding" can be classified under three definable headings [7-9]:

●Systemic disorders of hemostasis (AUB-C) – Von Willebrand Disease (VWD) is the most common of these; however, a number of other such disorders should be considered, particularly when a high index of suspicion for coagulopathy remains after negative tests for VWD.

●Ovulatory dysfunction (AUB-O) – Ovulatory dysfunction generally results from dysfunction in the hypothalamic-pituitary-ovarian axis, typically manifesting with amenorrhea or uterine bleeding with varying cycle duration and/or volume of blood flow.

●Primary endometrial dysfunction (AUB-E) – These disorders are primarily caused by disturbances in the molecular and cellular mechanisms responsible for regulation of the volume of blood lost at menstruation. Inflammatory or infectious endometrial disorders, such as chlamydial endometritis, are also included in this category.

Polyps (AUB-P) — For AUB-P, polyps (ie, localized epithelial tumors) are present as defined by sonohysterography and/or hysteroscopic imaging; histopathologic confirmation is not required for AUB-P classification. Absence of polyps is also documented. (See "Endometrial polyps" and "Benign cervical lesions and congenital anomalies of the cervix", section on 'Polyps'.)

Adenomyosis (AUB-A) — For AUB-A, a presumptive diagnosis of adenomyosis (ie, endometrial-type glands and stroma within the myometrium typically with surrounding myometrial hypertrophy or hyperplasia) can be made based on transvaginal ultrasound or magnetic resonance imaging (MRI); histopathologic confirmation is not required for AUB-A classification.

The role that adenomyosis plays in the genesis of AUB is poorly understood, as some studies have concluded that there is little or no role [32,33], while others describe an association with heavy menstrual bleeding (HMB) with or without dysmenorrhea [34-36]. (See "Uterine adenomyosis".)

Leiomyomas (AUB-L) — For AUB-L, leiomyomas (also referred to as myomas or fibroids) should be seen on pelvic imaging. Absence of leiomyomas is also documented.

There is a hierarchy for primary, secondary, and tertiary AUB-L classification based upon the FIGO Leiomyoma Subclassification System (figure 7B).

●Primary AUB-L classification is based on the presence of one or more leiomyomas by sonographic examination, regardless of the location, number, and size.

●Secondary AUB-L classification distinguishes myomas that abut the endometrium or distort the endometrial cavity (submucous leiomyomas [SM] [37]) from leiomyomas in other locations (O). This is because submucous lesions are most likely to contribute to AUB, although there is some evidence that intramural myomas may also contribute to the total menstrual blood loss [38]. The determination of whether there is a submucous leiomyoma is made using either hysterosonography or hysteroscopy.

●The tertiary AUB-L classification uses the FIGO Leiomyoma Subclassification System to categorize leiomyomas using numerals to identify their relationship to the endometrium, myometrium, and/or serosa (figure 7B and figure 6). It includes a category for lesions that are not related to the uterine corpus such as cervical and "parasitic" leiomyomas (ie, blood supply that arises from nonuterine sources) [7-9].

When a leiomyoma abuts or distorts both the endometrium and the serosa (hybrid), it is categorized first by the submucous categorization (numerals 0 to 3), then by the subserosal relationship (numerals 4 to 7), with these two numbers separated by a hyphen. The clinician or clinical investigator may also consider the size, number, and location (eg, fundal, cervical) of the leiomyomas in the uterus.

Uterine leiomyomas are discussed in detail separately. (See "Uterine fibroids (leiomyomas): Epidemiology, clinical features, diagnosis, and natural history".)

Malignancy and hyperplasia (AUB-M) — For AUB-M, patients should have histological documentation of endometrial hyperplasia with atypia or cancer of the uterine corpus. Subclassification is based on histology using the appropriate WHO system for hyperplasia, or the FIGO staging system for cancer [7-9,39,40]. (See "Endometrial hyperplasia: Clinical features, diagnosis, and differential diagnosis" and "Endometrial carcinoma: Clinical features, diagnosis, prognosis, and screening" and "Uterine sarcoma: Classification, epidemiology, clinical manifestations, and diagnosis".)

Coagulopathy (AUB-C) — For AUB-C, laboratory testing must confirm coagulopathy. The approach to identifying these patients starts with a structured history to assess symptoms or risk factors for coagulation disorders (table 5) [41]. (See "Abnormal uterine bleeding in nonpregnant reproductive-age patients: Evaluation and approach to diagnosis", section on 'Medical history'.)

Ovulatory dysfunction (AUB-O) — For AUB-O, the patient should not be on hormonal medication and should have a cycle length in the previous 6 to 12 months that varies by more than seven to nine days, depending on age, as described above (see 'Abnormalities in regularity' above). AUB-O is not used to classify ovulatory dysfunction caused by drug treatment, which are classified as AUB-I (iatrogenic causes). (See 'Iatrogenic causes (AUB-I)' below.)

AUB-O describes a patient who is not ovulating, has infrequent or irregular ovulation, or, especially in the late reproductive years, experiences luteal out-of-phase (“LOOP”) events [42]. These patients typically experience some combination of irregularity of bleeding and variable volume of menstrual blood loss, which in some cases manifests with volumes sufficient to be categorized as HMB. Many disorders may result in ovulatory dysfunction. (See "Abnormal uterine bleeding in nonpregnant reproductive-age patients: Evaluation and approach to diagnosis", section on 'Irregular bleeding'.)

Ovulatory dysfunction, including anovulation, may be associated with what appear to be normal cycle lengths (24 to 38 days) and regularity. Some data show a significant incidence of anovulation at all ages, sometimes even when cycles were deemed regular [43].

Endometrial dysfunction (AUB-E) — For AUB-E, patients have all of the following: predictable and cyclic menses suggestive of normal ovulation, HMB or intermenstrual bleeding (IMB), and no other definable causes for AUB [37]. The AUB-E is usually caused by a primary disorder of the endometrium.

If the symptom is HMB, the patient may have a primary disorder of mechanisms regulating local endometrial hemostasis [44-48]; there are no available tests for these disorders, so AUB-E is assigned after excluding other etiologies of AUB. AUB-E may be diagnosed even in the presence of other findings, such as adenomyosis or leiomyomas types 4 to 8 (figure 7B), as the latter are unlikely to contribute to the symptom of HMB.

AUB-E may also be caused by endometritis secondary to, for example, Chlamydia trachomatis [37,49].

Iatrogenic causes (AUB-I) — For AUB-I, the abnormal bleeding is attributed to medical devices (mainly intrauterine contraceptive systems), gonadal steroids but particularly progestogen-only preparations, or drug therapy. Medications that may cause AUB-I include:

●Gonadal steroids (eg, estrogens, progestins, androgens, and combined estrogen and progestin formulations).

●Pharmaceutical agents that affect gonadal steroid production or activity (eg, gonadotropin-releasing hormone analogues, aromatase inhibitors, selective estrogen receptor modulators, selective progesterone receptor modulators).

●Anticoagulants.

●Systemic agents that contribute to disorders of ovulation; for example, those that interfere with dopamine metabolism or cause hyperprolactinemia (table 6).

●Intrauterine devices used for contraception (hormonal or nonhormonal) or menstrual blood loss management (hormonal).

(See "Evaluation and management of unscheduled bleeding in individuals using hormonal contraception" and "Abnormal uterine bleeding and uterine pathology in patients on tamoxifen therapy" and "Management of bleeding in patients receiving direct oral anticoagulants" and "Causes of hyperprolactinemia".)

Not otherwise classified (AUB-N) — AUB-N encompasses additional entities, such as AUB in the context of a uterine scar defect or isthmocele, which is frequently present following a cesarean birth (cesarean scar defect) [50].

DOCUMENTATION — The two International Federation of Gynecology and Obstetrics (FIGO) AUB systems have been designed to facilitate investigation and to allow both categorization and documentation of the potential causes of AUB in the reproductive years. The formal approach for System 2, the PALM-COEIN System, follows the example of the World Health Organization tumor-node-metastasis staging of malignant tumors, with each component addressed for all patients, as illustrated in the figure (figure 7A-B).

Following appropriate investigation, a patient with AUB symptoms may be found to have one or multiple potential causes or contributors. A subscript of “1” means the condition is present, and “0” means it is absent; however, because full documentation might be considered to be cumbersome in clinical practice, the notation may be shortened to only the positive findings. For example, AUB-A, -Lo, -O means that the patient has adenomyosis, a leiomyoma that is “other” (not containing the endometrium, ie, subtype 4 to 8), and ovulatory dysfunction (figure 7B). AUB-P, -Lsm means that the patient has an endometrial polyp and a leiomyoma that is submucous, ie, subtype 0 to 3.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Abnormal uterine bleeding".)

SUMMARY

●Abnormal uterine bleeding (AUB) in females of reproductive age who are not pregnant comprises a common set of gynecologic symptoms. The varied use of terminology to describe AUB symptoms has led to difficulties in clinical and research communication and documentation. The International Federation of Gynecology and Obstetrics (FIGO) has developed two systems: one defining both normal menstrual bleeding and AUB symptoms (System 1) and a second for classification of potential causes of AUB (System 2, the PALM-COEIN [Polyp, Adenomyosis, Leiomyoma, Malignancy and hyperplasia, Coagulopathy, Ovulatory dysfunction, Endometrial disorders, Iatrogenic, and "Not otherwise classified"] system). (See 'Introduction' above.)

●Normal menstruation is defined as (table 1) (see 'Definition of normal uterine bleeding (menstruation)' above):

•Frequency – 24 to 38 days.

•Regularity – No more than 7 to 9 days difference between the shortest to longest cycles; cycle length is the number of days from the first day of one menstrual cycle to the first day of the next.

•Duration – Up to 8 days; duration is the number of days of bleeding in a single menstrual period.

•Volume – Clinical definition is subjective and defined as a volume that does not interfere with a patient's physical, social, emotional, and/or material quality of life; the research definition of normal volume is ≤80 mL menstrual "blood" loss per cycle.

●AUB is the term used to describe any symptomatic variation from normal menstruation (in terms of frequency, regularity, duration, or volume) and also includes intermenstrual bleeding and abnormal bleeding associated with the use of agents that impact endogenous gonadal steroidal production or activity. This term covers the full range of symptoms of abnormal bleeding (table 1). (See 'Definition of AUB' above.)

●In terms of severity and duration of symptoms, acute AUB is defined as an episode of uterine bleeding in a nonpregnant patient of reproductive age that, in the opinion of the clinician, is of sufficient quantity to require immediate intervention to reduce or prevent further blood loss. Chronic AUB is defined as uterine bleeding that is abnormal in frequency, regularity, duration, and/or volume and has been present for at least the majority of the past six months (algorithm 1). (See 'Definition of AUB' above.)

●FIGO AUB System 2, the classification system for AUB etiologies in reproductive-age patients, is stratified into nine basic categories that are arranged according to the acronym PALM-COEIN: polyp, adenomyosis, leiomyoma, malignancy and hyperplasia, coagulopathy, ovulatory dysfunction, endometrial dysfunction, iatrogenic, and "not otherwise classified." (See 'FIGO AUB System 2: PALM-COEIN classification of potential causes of AUB in the reproductive years' above.)

●The PALM-COEIN system has a subclassification system for uterine leiomyoma presence based upon relationships to the endometrium, uterine serosa, and myometrium (figure 7B and figure 6). (See 'Leiomyomas (AUB-L)' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Ian Fraser, AO, DSc, MD, who contributed to an earlier version of this topic review.