Dysfunctional uterine bleeding (DUB), a nonspecific term for abnormal uterine bleeding (AUB), is classically defined as excessively heavy, prolonged, or frequent bleeding of uterine origin that is not caused by pregnancy or recognizable pelvic or systemic disease. [1, 2] It usually results from disordered functioning of the hypothalamic-pituitary-ovarian (HPO) axis and is often associated with anovulatory cycles.
This classic definition has proved less useful because of the current understanding of the pathophysiology of DUB. However, it does highlight that anovulatory uterine bleeding (as part of the etiology spectrum of DUB) is a diagnosis of exclusion.
DUB occurs most often in women in the beginning and end of their reproductive years: 20% of cases occur in adolescent females, and as many as 50% of women aged 40-50 years experience DUB.  Of these cases of AUB, about 90% are due to menstrual periods when ovulation does not occur. Adolescent females have several anovulatory cycles per year; hence, anovulatory uterine bleeding is the primary cause of DUB in the female adolescent population. [4, 5, 6, 7]
Some have argued that the term DUB should be retired and that AUB, appropriately qualified, should be used instead. AUB, as described by the International Federation of Gynecology and Obstetrics (FIGO), can be classified according to the PALM-COEIN system, in which the acronym PALM represents structural causes (polyps, adenomyosis, leiomyomas, malignancy and hyperplasia) and the acronym COEIN represents nonstructural causes (coagulopathy, ovulatory dysfunction, endometrial, iatrogenic, and not yet classified). 
In the PALM-COEIN system, for example, AUB from ovulatory dysfunction would be designated as AUB-O. The following discussion, however, continues to use the term DUB.
The normal menstrual cycle, characterized by sequential growth, maturation, and eventual sloughing of the endometrial mucosa, is produced by the cyclic release of estrogen and progesterone from the ovary. This occurs (orchestrated by the HPO axis) with amazing regularity throughout most of a woman's reproductive lifetime.
An understanding of the normal cyclic fluctuations of the two gonadotropins (ie, luteinizing hormone [LH] and follicle-stimulating hormone [FSH]) and the primary female reproductive hormones (ie, estrogen and progesterone) helps clarify the derangements associated with anovulation. 
The first 14 days of a typical 28-day menstrual cycle (day 1 being defined as the first day of menstrual flow) are characterized by rising FSH levels, which stimulate ovarian follicle development and the subsequent production of estrogens (primarily estradiol). Serum progesterone levels are extremely low during this stage. LH levels climb more slowly but abruptly peak on day 12 or 13 in positive response to rising estrogen levels. (See the image below.)
During that first 14-day period, the endometrium, under the influence of estrogen, undergoes proliferation. The LH surge stimulates ovulation (on or about day 14) and conversion of the ovulatory follicle to a corpus luteum, which is responsible for estrogen and progesterone production. Under the influence of this progesterone, the endometrium is converted to a secretory state in preparation for implantation if fertilization of the ovum should occur. Progesterone is produced only if ovulation occurs.
As LH levels drop (on the assumption that fertilization and production of human chorionic gonadotropin [HCG] by the developing conceptus did not occur), the corpus luteum regresses, estrogen and progesterone levels plummet, and the endometrium deteriorates and is sloughed.
The average menstrual cycle is 28-29 days (range, 21-35 days). Initially, some teenagers can have cycles as long as 45 days. Over time, the menstrual cycle becomes fairly consistent from month to month in any given woman. Normal menstrual flow lasts for 7 days or less and produces an average total blood loss of 25-69 mL. Bleeding more frequently than every 21 days or less frequently than 45 days, menstrual flow longer than 7 days, and blood loss exceeding 80 mL are considered abnormal.
With anovulation, estrogen levels rise as usual in the early phase of the cycle. In the absence of ovulation, a corpus luteum never forms and progesterone is not produced. The endometrium moves into a hyperproliferative state, ultimately outgrowing its estrogen supply. This leads to irregular sloughing of the endometrium and excessive bleeding from spiral arteries that have not undergone physiologic senescence.
The exact incidence of DUB is unknown. The understanding of the epidemiology comes from case series reports from tertiary institutions with patients who are unlikely to reflect the general population. Nearly half of all women have irregular periods in the first year after menarche, and more than half of the cycles are anovulatory. Irregular periods can persist for as long as 5 years after menarche in 20% of women. 
International rates should reflect those of the United States.
The main complication of DUB is anemia. For female adolescents, anemia is indicated when the hemoglobin level is less than 12 g/dL (normal range, 12.1-15.1 g/dL). Acute blood loss can occasionally lead to a profound anemia. Blood product transfusion (with the attendant risks and complications) is occasionally required.
Chronic or recurrent DUB can result in an iron-deficient state.
Blood loss in the healthy female adolescent is rarely of a fatal magnitude.
Race does not seem to contribute significantly to the incidence of DUB.
Worldwide, the age of menarche varies, influenced by female biology, genetic factors, and environmental factors. Geographic region, race, and ethnicity play significant roles. The median age of menarche worldwide is estimated at 14 years, with the premise that menarche occurs later in Asian populations than in populations from the Western hemisphere. 
In the United States, the average age of menarche is 12.3 years.  In Canada and the United Kingdom, the average ages of menarche are 12.7 years and 12.9 years, respectively. [13, 14] Irregular and anovulatory cycles may persist for a range of 1-5 years after the onset of menstrual periods; however, regulation of menstrual periods typically occurs within 2 years after menarche.
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