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BACKGROUND

Abnormal uterine bleeding (AUB) is a common cause for concern in adolescents and often results in visits to healthcare providers and emergency departments.1 Abnormal uterine bleeding is defined as excessively heavy, frequent, and/or prolonged bleeding from the uterine endometrium.2,3 AUB includes menstrual cycles that occur less than 21 or more than 45 days apart, bleeding that lasts more than 8 days, or blood loss greater than 80 mL.1,2,4 AUB can present as heavy and prolonged bleeding with associated periods of amenorrhea or frequent and excessive bleeding that occurs every 1 to 2 weeks.4 Heavy menstrual bleeding (HMB) refers to excessive blood loss (>80 mL) regardless of the underlying menstrual pattern.5

PATHOPHYSIOLOGY

It is important to review normal menstruation in order to understand the pathophysiology that leads to abnormal uterine bleeding. The menstrual cycle consists of the follicular, ovulatory, and luteal phases. It requires a fully functioning hypothalamic-pituitary-ovarian (HPO) axis. During the follicular phase, which lasts between 7 and 21 days, the hypothalamus initiates pulsatile release of gonadotropin-releasing hormone (GnRH), which in turn stimulates the pituitary to release FSH (FSH) and luteinizing hormone (LH). FSH stimulates ovarian follicle development and LH stimulates the ovaries to secrete estrogen and androgens. As estrogen concentrations rise, they stimulate endometrial proliferation. Estrogen exerts positive feedback on LH secretion, leading to the midcycle LH surge, which then leads to ovulation. During the ovulatory phase, a mature ovarian follicle releases an oocyte and then becomes a functioning corpus luteum. The luteal phase begins after ovulation and typically lasts 14 days. During this time the corpus luteum produces progesterone, which helps to stabilize the endometrial lining and promote growth of blood vessels and glandular tissue. If fertilization does not occur, the corpus luteum involutes and the subsequent drop in progesterone leads to sloughing of the endometrial lining.2,6,7

The median age of menarche is between 12 and 13 years of age and typically occurs within 2 to 3 years of thelarche, at Tanner stage IV for breast development.8,9 In the first gynecologic year, the mean cycle interval is 32 days, with 90% of cycles occurring 21 to 45 days apart and typically lasting less than 8 days, with average blood loss of 30 to 40 mL.2,8 This cycle variability reflects the fact that many menstrual cycles in the early menarchal years are anovulatory.

Immaturity of the HPO axis, resulting in anovulatory cycles, is the most common cause of AUB in adolescents within 4 years of menarche. Until this axis is fully mature, ovulation may not occur each month. In fact, up to 85% of all cycles are anovulatory in the first year after menarche and 30% to 50% remain anovulatory 4 years after menarche.4,5 Without ovulation, there is no corpus luteum or associated progesterone ...

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