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Abnormal uterine bleeding (AUB), formerly known as Dysfunctional Uterine Bleeding (DUB), is defined as heavy menstrual bleeding and/or intermenstrual bleeding. AUB can caused by structural and nonstructural etiologies, with specific types of AUB categorized by the PALM-COEIN classification system, which was introduced in 2011 by the International Federation of Gynecology and Obstetrics (FIGO).

While "dysfunctional uterine bleeding" is often used in the literature to denote AUB without a structural cause, discontinuation of its use is recommended.

The PALM-COEIN classification system
Each letter of the PALM-COEIN system represent a distinct cause of AUB, which are subdivided into either structural (PALM) or nonstructural (COEIN) causes.

Structural causes

 * P = Polyp (AUB-P)
 * A = Adenomyosis (AUB-A)
 * L = Leiomyoma (AUB-L)
 * M = Malignancy and hyperplasia (AUB-M)

Non-structural causes

 * C = Coagulopathy (AUB-C). This includes inherited conditions, such as von Willebrand disease, and acquired conditions, such as the use of warfarin or heparin use.
 * O = Ovulatory dysfunction (AUB-O). This encompasses a range of dysfunctional bleeding presentations, with the common mechanism being unopposed estrogen in the setting of an intact hypothalamic-pituitary-ovarian axis. This includes polycystic ovarian disease, increased local fibrinolytic activity, abnormal prostaglandin synthesis and receptor upregulation, and increased tissue plasminogen activator activity.
 * E = Endometrial (AUB-E).
 * I = Iatrogenic (AUB-I)
 * N = Not yet classified (AUB-N)

It is usually due to hormonal disturbances: reduced levels of progesterone causes low levels of prostaglandin F2alpha and causes menorrhagia; increased levels of tissue plasminogen activator (TPA) (a fibrinolytic enzyme) leads to more fibrinolysis.

Diagnosis must be made by exclusion, since organic pathology must first be ruled out.

It can be classified as ovulatory or anovulatory, depending on whether ovulation is occurring or not.

Some sources state that the term implies a hormonal mechanism.

Ovulatory DUB
10% of cases occur in women who are ovulating, but progesterone secretion is prolonged because estrogen levels are low. This causes irregular shedding of the uterine lining and break-through bleeding. Some evidence has associated Ovulatory DUB with more fragile blood vessels in the uterus.

It may represent a possible endocrine dysfunction, resulting in menorrhagia or metrorrhagia. Mid-cycle bleeding may indicate a transient estrogen decline, while late-cycle bleeding may indicate progesterone deficiency.

Anovulatory DUB
About 90% of DUB events occur when ovulation is not occurring (Anovulatory DUB). Anovulatory menstrual cycles are common at the extremes of reproductive age, such as early puberty and perimenopause (period around menopause). In such cases, women do not properly develop and release a mature egg. When this happens, the corpus luteum, which is a mound of tissue that produces progesterone, does not form. As a result, estrogen is produced continuously, causing an overgrowth of the uterus lining. The period is delayed in such cases, and when it occurs menstruation can be very heavy and prolonged. Sometimes anovulatory DUB is due to a delay in the full maturation of the reproductive system in teenagers. Usually, however, the mechanisms are unknown.

The etiology can be psychological stress, weight (obesity, anorexia, or a rapid change), exercise, endocrinopathy, neoplasm, drugs, or it may be otherwise idiopathic.

Assessment of anovulatory DUB should always start with a good medical history and physical examination. Laboratory assessment of hemoglobin, luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin, T4, thyroid stimulating hormone (TSH), pregnancy (by βhCG), and androgen profile should also happen. More extensive testing might include an ultrasound and endometrial sampling.

Management
Drug of choice is progesterone. Management of dysfunctional uterine bleeding predominantly consists of reassurance, though mid-cycle estrogen and late-cycle progestin can be used for mid- and late-cycle bleeding respectively.

Also, non-specific hormonal therapy such as combined high-dose estrogen and high-dose progestin can be given. Ormeloxifene is a non-hormonal medication that treats DUB but is only legally available in India.

The goal of therapy should be to arrest bleeding, replace lost iron to avoid anemia, and prevent future bleeding.

A hysterectomy may be performed in some cases.