NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health. De Groot LJ, Chrousos G, Dungan K, et al., editors. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.; 2000-. The Normal Menstrual Cycle and the Control of Ovulation Beverly G Reed, MD and Bruce R Carr, MD. Last Update: May 22, 2015. ABSTRACT Menstruation is the cyclic, orderly sloughing of the uterine lining, in response to the interactions of hormones produced by the hypothalamus, pituitary, and ovaries. The menstrual cycle may be divided into two phases: (1) follicular or proliferative phase, and (2) the luteal or secretory phase.The length of a menstrual cycle is the number of days between the first day of menstrual bleeding of one cycle to the onset of menses of the next cycle. The median duration of a menstrual cycle is 28 days with most cycle lengths between 25 to 30 days [1-3]. Patients who experience menstrual cycles that occur at intervals less than 21 days are termed polymenorrheic, while patients who experience prolonged menstrual cycles greater than 35 days, are termed oligomenorrheic. The typical volume of blood lost during menstruation is approximately 30 mL . Any amount greater than 80 mL is considered abnormal . The menstrual cycle is typically most irregular around the extremes of reproductive life (menarche and menopause) due to anovulation and inadequate follicular development [5-7]. The luteal phase of the cycle is relatively constant in all women, with a duration of 14 days. The variability of cycle length is usually derived from varying lengths of the follicular phase of the cycle, which can range from 10 to 16 days. For complete coverage of this and related topics, please visit . TAKE HOME POINTS The length of a menstrual cycle is the number of days between the first day of menstrual bleeding of one cycle to the onset of menses of the next cycle. The median duration of a menstrual cycle is 28 days with most cycle lengths between 25 to 30 days. The menstrual cycle may be divided into two phases: (1) follicular or proliferative phase, and (2) the luteal or secretory phase. The follicular phase begins from the first day of menses until ovulation. The development of ovarian follicles characterize this phase. The LH surge is initiated by a dramatic rise of estradiol produced by the preovulatory follicle and results in subsequent ovulation. The LH surge stimulates luteinization of the granulosa cells and stimulates the synthesis of progesterone responsible for the midcycle FSH surge. Also, the LH surge stimulates resumption of meiosis and the completion of reduction division in the oocyte with the release of the first polar body. The luteal phase is 14 days long in most women. If the corpus luteum is not rescued by pregnancy, it will demise. The resultant progesterone withdrawal results in menses.
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