Menstrual cycle
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The menstrual cycle is a recurring cycle of physiologic changes that occurs in the females of several mammals, including human beings and other apes.<ref name="kippley">Modèle:Cite book</ref>
Menstrual cycles are counted from the first day of menstrual flow, because the onset of menstruation corresponds closely with the hormonal cycle. The menstrual cycle may be divided into several phases, and the length of each phase varies from woman to woman and cycle to cycle. Average values are shown below:
| Name of phase | Days |
| menstrual phase | 1–4 |
| follicular phase (also known as proliferative phase) | 5–13 |
| ovulation (not a phase, but an event dividing phases) | 14 |
| luteal phase (also known as secretory phase) | 15–26 |
| ischemic phase (some sources group this with secretory phase) | 27–28 |
www.americanpregnancy.org/gettingpregnant/understandingovulation.html</ref>) After ovulation the remains of the dominant follicle in the ovary become a corpus luteum; this body has a primary function of producing large amounts of progesterone. Under the influence of progesterone, the endometrium (uterine lining) changes to prepare for potential implantation of an embryo to establish a pregnancy. If implantation does not occur within approximately two weeks, the corpus luteum will die, causing sharp drops in levels of both progesterone and estrogen. These hormone drops cause the uterus to shed its lining in a process termed menstruation.//www.americanpregnancy.org/gettingpregnant/understandingovulation.html</ref>) After ovulation the remains of the dominant follicle in the ovary become a corpus luteum; this body has a primary function of producing large amounts of progesterone. Under the influence of progesterone, the endometrium (uterine lining) changes to prepare for potential implantation of an embryo to establish a pregnancy. If implantation does not occur within approximately two weeks, the corpus luteum will die, causing sharp drops in levels of both progesterone and estrogen. These hormone drops cause the uterus to shed its lining in a process termed menstruation.
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Phases of the menstrual cycle
Menstruation
Menstruation is also called menstrual bleeding, menses, a period or catamenia. The flow of menses normally serves as a sign that a woman has not become pregnant. (However, this cannot be taken as certainty, as sometimes there is some bleeding in early pregnancy.) During the reproductive years, failure to menstruate may provide the first indication to a woman that she may have become pregnant.
Eumenorrhea denotes normal, regular menstruation that lasts for a few days (usually 3 to 5 days, but anywhere from 2 to 7 days is considered normal).<ref name="spermlife">Modèle:Cite journal</ref><ref name="JIndianMedAssoc1993-Billings">Modèle:Cite journal</ref> The most fertile period (the time with the highest likelihood of pregnancy resulting from sexual intercourse) covers the time from some 5 days before ovulation until 1–2 days after ovulation. In an average 28 day cycle with a 14-day luteal phase, this corresponds to the second and the beginning of the third week of the cycle. Fertility awareness methods of birth control attempt to determine the precise time of ovulation in order to find the relatively fertile and the relatively infertile days in the cycle.
People who have heard about the menstrual cycle and ovulation often mistakenly assume, for contraceptive purposes, that menstrual cycles regularly take 28 days, and that ovulation always occurs 14 days after beginning of the menses. This assumption may lead to unintended pregnancies. Note too that not every event of bleeding counts as a menstruation, and this can mislead people in their calculation of the fertile window.
If a woman wants to conceive, the most fertile time occurs between 19 and 10 days prior to the expected menses. Many women use ovulation detection kits that detect the presence of the LH surge in the urine to indicate the most fertile time. Other ovulation detection systems rely on observation of one or more of the three primary fertility signs (basal body temperature, cervical fluid, and cervical position).
Among women living closely together, the onsets of menstruation may tend to synchronise somewhat. This McClintock effect was first described in 1971, and possibly explained by the action of pheromones in 1998.<ref name="Mclintock">Modèle:Cite journal</ref> However, subsequent research has called this conclusion into question.<ref>Modèle:Cite journal</ref>, while another has found male-initiated sex to occur at a constant rate throughout the menstrual cycle.<ref name="tcoyf">Modèle:Cite book</ref>
Anovulatory bleeding may occur on a regular basis, but more commonly happens with irregular frequency. Anovulatory flow commonly occurs prior to menopause (premenopause) or in women with polycystic ovary syndrome.
Infrequent or irregular ovulation is called oligoovulation.
Flow
Sudden heavy flows or amounts in excess of 80 ml (hypermenorrhea or menorrhagia) are not normal.
Very little flow (less than 10ml) is called hypomenorrhea.
Prolonged flow (metrorrhagia, also meno-metrorrhagia) no longer shows a clear interval pattern. Dysfunctional uterine bleeding refers to hormonally caused flow abnormalities, typically anovulation.
All bleeding abnormalities need medical attention; they may indicate hormone imbalances, uterine fibroids, or other problems. As pregnant patients may bleed, a pregnancy test forms part of the evaluation of abnormal flow.
Cycle length
The medical term for cycles with intervals of 21 days or fewer is polymenorrhea and, on the other hand, the term for cycles with intervals exceeding 35 days is oligomenorrhea (or amenorrhea if intervals exceed 180 days).
Amenorrhea refers to a prolonged absence of menses during the reproductive years of a woman. For example, women with very low body fat, such as athletes, may cease to menstruate. Amenorrhea also occurs during pregancy.
Early menarche
The condition precocious puberty has caused menstruation to occur in girls as young as eight months old.<!--
www.snopes.com/pregnant/medina.asp | accessdate = 2006-07-02 }}</ref>//www.snopes.com/pregnant/medina.asp | accessdate = 2006-07-02 }}</ref>
Contraception and menstruation
Hormonal options
Estrogens and progesterone-like hormones make up the main active ingredients of hormonal birth control methods such as the pill. Typically they cause regular monthly flow that roughly mimics a menstrual cycle in appearance, but suppresses ovulation. With most pills, a woman takes hormone pills for 21 days, followed by 7 days of non-functional placebo pills or no pills at all, then the cycle starts again. During the 7 placebo days, a withdrawal bleeding occurs; this differs from ordinary menstruation, and skipping the placebos and continuing with the next batch of hormone pills may suppress it. (There are two main versions of the pill: monophasic and triphasic. With triphasic pills, skipping placebos and continuing with the next month's dose can make a woman more likely to experience spotting or breakthrough bleeding.) In 2003, the U.S. Food and Drug Administration (FDA) approved low-dose monophasic birth control pills that induce withdrawal bleeding every 3 months. Yet another version of the pill is the Loestrin Fe, which has only a four-day placebo "week" (the placebos are actually iron supplements intended to replenish iron lost by uterine shedding); the other three placebos are replaced with active hormone pills. This system is intended to help shorten periods. Mircette contains several days of estrogen-only pills in addition to the usual combination estrogen/progestin pills, in the case of women who may have problems with low estrogen during the placebo days with other pills.
Other types of hormonal birth control which affect menstruation include the vaginal Nuvaring and the transdermal patch (like the standard pill pack, active hormones are given for three weeks, followed by a one-week break for bleeding) and the injection (which can eliminate all flow as long as the injections are taken every twelve weeks, although spotting is a common side effect).
Effects on menstruation
All such methods are designed to regulate monthly bleeding. Because of this, they are often chosen by females who wish to regulate the frequency and length of their period, often for basic convenience and especially when such factors are irregular and problematic on their own. Hormonal contraception has also been shown to improve menstrual factors such as cramping, heavy flow, and other bothersome physical and emotional issues related to periods.
Control and flexibility
Hormonal methods which are controlled by the user day-to-day, including pills, the ring, and the patch, need not always be used according to the standard cycle/calendar. Their use can be rescheduled and altered in various ways to postpone or skip periods when desired for reasons of convenience (e.g., traveling or scheduled gynecological exams), personal enjoyment (such as expected sexual encounters or events like a wedding or dance), or health (including very painful periods or sensitivity to hormone fluctuations). Similarly, abrupt cessation of use can induce a breakthrough period mid-cycle.
Other contraceptive methods
Most IUDs are not designed to affect menstruation or breakthrough bleeding, but may exacerbate cramps or the heaviness of the flow due to their placement within the uterus. The Mirena IUD releases a small continuous dosage of a progesterone-like hormone, which can sometimes cause menstruation to cease. Tubal sterilization alone will not affect menstruation, though the ablation option often performed at the same time will cause menstruation to cease. Hysterectomy will, of course, completely stop menstruation as it entails the removal of the uterus (and sometimes the ovaries, fallopian tubes, and cervix). Fertility awareness methods do not affect the period in and of themselves, but involve careful observation of various kinds, of which the timing of the period is an essential factor.
Menstruation and the moon
See also: Culture and menstruation
www.findarticles.com/p/articles/mi_m0ISW/is_259-260/ai_n10299307/pg_1]</ref>//www.findarticles.com/p/articles/mi_m0ISW/is_259-260/ai_n10299307/pg_1]</ref>
The word "menstruation" is etymologically related to moon. The terms "menstruation" and "menses" come from the Latin mensis (month), which in turn relates to the Greek mene (moon) and to the roots of the English words month and moon — reflecting the fact that the moon also takes close to 28 days to revolve around the Earth (actually 27.32 days). The synodical lunar month, the period between two new moons (or full moons), is 29.53 days long.
www.westonaprice.org/women/fertility.html Fertility Awareness,//www.westonaprice.org/women/fertility.html Fertility Awareness, Food, and Night-Lighting]". Wise Traditions in Food, Farming and the Healing Arts, Spring 2004. See section on Night-Lighting.</ref> and animals<ref>Harder, Ben. Bright nights kindle cancers in mice. Science News, Week of Aug. 28, 2004; Vol. 166, No. 9 , p. 141.</ref> have found that artificial light at night does influence the menstrual cycle in humans and the estrus cycle in mice (cycles are more regular in the absence of artificial light at night), though none have duplicated the synchronization of women's menstrual cycles with the lunar cycle. One author has suggested that sensitivity of women's cycles to nightlighting is caused by nutritional deficiencies of certain vitamins and minerals.<ref>Shannon, Marilyn. Fertility, Cycles, and Nutrition. Cincinnati, Ohio: The Couple to Couple League International, 2001. pp. 71–72.</ref>
www.straightdope.com/classics/a990924.html "What's the link between the moon and menstruation?"] (accessed 6 June 2006): Modèle:Cite book</ref><ref>Cutler WB. Lunar and menstrual phase locking. Am J Obstet Gynecol. 1980 Aug 1;137(7):834-9. PMID: 7405975.
Friedmann E. Menstrual and lunar cycles. Am J Obstet Gynecol. 1981 Jun 1;140(3):350. PMID: 7246643
Law SP. The regulation of menstrual cycle and its relationship to the moon. Acta Obstet Gynecol Scand. 1986;65(1):45-8. PMID: 3716780
Zimecki M. The lunar cycle: effects on human and animal behavior and physiology. Postepy Hig Med Dosw (Online). 2006;60:1–7. Review.//www.straightdope.com/classics/a990924.html "What's the link between the moon and menstruation?"] (accessed 6 June 2006): Modèle:Cite book</ref><ref>Cutler WB. Lunar and menstrual phase locking. Am J Obstet Gynecol. 1980 Aug 1;137(7):834-9. PMID: 7405975.
Friedmann E. Menstrual and lunar cycles. Am J Obstet Gynecol. 1981 Jun 1;140(3):350. PMID: 7246643
Law SP. The regulation of menstrual cycle and its relationship to the moon. Acta Obstet Gynecol Scand. 1986;65(1):45-8. PMID: 3716780
Zimecki M. The lunar cycle: effects on human and animal behavior and physiology. Postepy Hig Med Dosw (Online). 2006;60:1–7. Review.
PMID: 16407788</ref>
Menstrual cycles in other mammals
Females of most species advertise ovulation to males with visual cues and behavioral cues, pheromones, or both (humans are a notable exception). This period of advertised fertility is known as estrus or heat. However, in animals with menstrual cycles, females can be sexually active at any time in their cycle, even when they are not in heat. Great apes' cycles vary in length from an average of 29 days in orangutans to an average of 37 days in chimpanzees.
By contrast, in species that have estrous cycles rather than menstrual cycles, females are only receptive to copulation while they are in heat (dolphins are a notable exception). The other significant difference is that in an estrous cycle, if no fertilization takes place, the uterus reabsorbs the endometrium: no menstrual bleeding occurs. Some animals, such as domestic cats and dogs, experience small amounts of bleeding while in heat. This phase of the estrous cycle corresponds most closely to the follicular phase of the menstrual cycle and should not be confused with menstruation.
References
Notes
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External links
mum.org/ Museum of Menstruation and Women's Health]//mum.org/ Museum of Menstruation and Women's Health] mum.org/ Museum of Menstruation and Women's Health]//www.cemcor.ubc.ca/ Centre for Menstrual Cycle and Ovulation Research]
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