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Menstruation
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== Characteristics == {{Further|Menstrual cycle}} ===Length and duration=== The first menstrual period occurs after the onset of pubertal growth, and is called [[menarche]]. The average age of menarche is 12 to 15 years.<ref name="Jones2011"/><ref>{{cite journal | vauthors = Karapanou O, Papadimitriou A | title = Determinants of menarche | journal = Reproductive Biology and Endocrinology | volume = 8 | pages = 115 | date = September 2010 | pmid = 20920296 | pmc = 2958977 | doi = 10.1186/1477-7827-8-115 | doi-access = free }}</ref> However, it may occur as early as eight.<ref name="Women2014Men"/> The average age of the first period is generally later in the [[developing world]], and earlier in the [[developed world]].<ref name=Diaz2006/><ref name="pmid29778270">{{cite journal | vauthors = Alvergne A, HΓΆgqvist Tabor V | title = Is Female Health Cyclical? Evolutionary Perspectives on Menstruation | journal = Trends in Ecology & Evolution | volume = 33 | issue = 6 | pages = 399β414 | date = June 2018 | pmid = 29778270 | doi = 10.1016/j.tree.2018.03.006 | arxiv = 1704.08590 | bibcode = 2018TEcoE..33..399A | s2cid = 4581833 }}</ref> The average age of menarche has changed little in the United States since the 1950s.<ref name=Diaz2006/> Menstruation is the most visible phase of the [[menstrual cycle]] and its beginning is used as the marker between cycles. The first day of menstrual bleeding is the date used for the last menstrual period (LMP). The typical length of time between the first day of one period and the first day of the next is 21 to 45 days in young women, and 21 to 35 days in adults.<ref name="Women2014Men"/><ref name="Diaz2006" /> The average menstrual cycle length is conventionally said to be 28 days.<ref name="Women2014Men"/><ref name=Diaz2006>{{cite journal | vauthors = Diaz A, Laufer MR, Breech LL | title = Menstruation in girls and adolescents: using the menstrual cycle as a vital sign | journal = Pediatrics | volume = 118 | issue = 5 | pages = 2245β2250 | date = November 2006 | pmid = 17079600 | doi = 10.1542/peds.2006-2481 | s2cid = 37802775 | doi-access = }}</ref> In the largest-ever study using data from menstrial apps, the mean menstrual cycle length in fact came to 29.3 days.<ref name=":6">{{cite journal | vauthors = Bull JR, Rowland SP, Scherwitzl EB, Scherwitzl R, Danielsson KG, Harper J | title = Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles | journal = npj Digital Medicine | volume = 2 | issue = 1 | pages = 83 | date = 2019-08-27 | pmid = 31482137 | pmc = 6710244 | doi = 10.1038/s41746-019-0152-7 }}</ref> The variability of menstrual cycle lengths is highest for women under 25 years of age and is lowest, that is, most regular, for ages 25 to 39 years.<ref name="Chiazze1968">{{cite journal | vauthors = Chiazze L, Brayer FT, Macisco JJ, Parker MP, Duffy BJ | title = The length and variability of the human menstrual cycle | journal = JAMA | volume = 203 | issue = 6 | pages = 377β380 | date = February 1968 | pmid = 5694118 | doi = 10.1001/jama.1968.03140060001001 }}</ref> The variability increases slightly for women aged 40 to 44 years.<ref name="Chiazze1968" /> [[Perimenopause]] is when a woman's fertility declines, and menstruation occurs less regularly in the years leading up to the final menstrual period, when a woman stops menstruating completely and is no longer fertile. The medical definition of [[menopause]] is one year without a period and typically occurs between 45 and 55 years in Western countries.<ref name="NIH2013Def" /><ref name = "Carlson_2004">{{cite book |vauthors= Carlson KJ, Eisenstat SA, Ziporyn TD |title = The new Harvard guide to women's health | year = 2004 | publisher = Harvard University Press | location = Cambridge, Massachusetts | isbn = 0-674-01343-3 | url-access = registration | url = https://archive.org/details/newharvardguidet00carl }}</ref>{{rp|381}} Menopause before age 45 is considered ''premature'' in industrialized countries.<ref>{{cite web|title=Clinical topic β Menopause|url=http://www.cks.nhs.uk/menopause#-292420|url-status=dead|archive-url=https://web.archive.org/web/20090707095123/http://www.cks.nhs.uk/menopause#-292420|archive-date=7 July 2009|access-date=2 November 2009|work=NHS}}</ref> Illnesses, certain surgeries, or medical treatments may cause menopause to occur earlier than it might have otherwise.<ref name="pmid31027683">{{cite journal | vauthors = Mishra GD, Chung HF, Cano A, Chedraui P, Goulis DG, Lopes P, Mueck A, Rees M, Senturk LM, Simoncini T, Stevenson JC, Stute P, Tuomikoski P, Lambrinoudaki I | display-authors = 6 | title = EMAS position statement: Predictors of premature and early natural menopause | journal = Maturitas | volume = 123 | issue = | pages = 82β88 | date = May 2019 | pmid = 31027683 | doi = 10.1016/j.maturitas.2019.03.008 | hdl-access = free | s2cid = 87361924 | hdl = 10138/318039 }}</ref> ===Menstrual fluid=== [[File:Menstrual fluid in cup 2nd day 40s female.jpg|thumb|[[Menstrual cup]] filled with menstrual fluid]] The average volume of menstrual fluid during a monthly menstrual period is {{convert|35|ml|UStbsp}} with {{convert|10|-|80|ml|UStbsp}} considered typical. ''Menstrual fluid'' is the correct term for the flow, although many people prefer to refer to it as "menstrual blood". Menstrual fluid is reddish-brown, a slightly darker color than venous blood.<ref name = "Carlson_2004" />{{rp|381}} About half of menstrual fluid is blood. This blood contains sodium, calcium, phosphate, iron, and chloride, the extent of which depends on the woman. As well as blood, the fluid consists of cervical mucus, vaginal secretions, and [[Endometrium|endometrial tissue]]. Vaginal fluids in menses mainly contribute water, common electrolytes, organ moieties, and at least 14 proteins, including glycoproteins.<ref>{{cite book| vauthors = Farage M |title=The Vulva: Anatomy, Physiology, and Pathology|date=22 Mar 2013|publisher=CRC Press|pages=155β158}}</ref> Many women and girls notice [[blood clots]] during menstruation. These appear as clumps of blood that may look like tissue. If there was a [[miscarriage]] or a [[stillbirth]], examination under a microscope can confirm if it was endometrial tissue or pregnancy tissue ([[products of conception]]) that was shed.<ref>{{cite web|title=Menstrual blood problems: Clots, color and thickness|url=http://women.webmd.com/menstrual-blood-problems-clots-color-and-thickness|website=WebMD|access-date=20 September 2011|url-status=live|archive-url=https://web.archive.org/web/20110923151848/http://women.webmd.com/menstrual-blood-problems-clots-color-and-thickness|archive-date=23 September 2011|df=dmy-all}}</ref> Sometimes menstrual clots or shed endometrial tissue is incorrectly thought to indicate an early-term miscarriage of an embryo. An [[enzyme]] called [[plasmin]] β contained in the endometrium β tends to inhibit the blood from [[blood clotting|clotting]].<ref>{{citation|author=C. J. Dockeray, B. L. Sheppard, L. Daly, J. Bonnar |date=April 1987 |doi=10.1016/0028-2243(87)90156-0 |issn=0301-2115 |issue=4 |pages=309β318 |periodical=European Journal of Obstetrics, Gynecology, and Reproductive Biology |pmid=2953634 |title=The fibrinolytic enzyme system in normal menstruation and excessive uterine bleeding and the effect of tranexamic acid |url=https://pubmed.ncbi.nlm.nih.gov/2953634/ |volume=24}}<!-- auto-translated from German by Module:CS1 translator --></ref> The amount of iron lost in menstrual fluid is relatively small for most women.{{better source needed|date=February 2021}}<ref>{{cite web |title=Iron-deficiency is not something you get just for being a lady | vauthors = Clancy K |url=http://blogs.scientificamerican.com/context-and-variation/2011/07/27/iron-deficiency-anemia/ |publisher=SciAm |date=27 July 2011 |url-status=live |archive-url=https://web.archive.org/web/20120317152812/http://blogs.scientificamerican.com/context-and-variation/2011/07/27/iron-deficiency-anemia/ |archive-date=17 March 2012 |df=dmy-all }}</ref> In one study, premenopausal women who exhibited symptoms of [[iron deficiency (medicine)|iron deficiency]] were given [[Endoscopy|endoscopies]]. 86% of them actually had [[gastrointestinal disease]] and were at risk of being misdiagnosed simply because they were menstruating.{{primary source inline|date=February 2021}}<ref>{{cite journal | vauthors = Kepczyk T, Cremins JE, Long BD, Bachinski MB, Smith LR, McNally PR | title = A prospective, multidisciplinary evaluation of premenopausal women with iron-deficiency anemia | journal = The American Journal of Gastroenterology | volume = 94 | issue = 1 | pages = 109β115 | date = January 1999 | doi = 10.1111/j.1572-0241.1999.00780.x | pmid = 9934740 | s2cid = 25975251 }}</ref> Heavy menstrual bleeding, occurring monthly, can result in [[anemia]].<ref>{{cite journal | vauthors = Mansour D, Hofmann A, Gemzell-Danielsson K | title = A Review of Clinical Guidelines on the Management of Iron Deficiency and Iron-Deficiency Anemia in Women with Heavy Menstrual Bleeding | journal = Advances in Therapy | volume = 38 | issue = 1 | pages = 201β225 | date = January 2021 | pmid = 33247314 | pmc = 7695235 | doi = 10.1007/s12325-020-01564-y }}</ref> ===Hormonal changes=== {{excerpt|menstrual cycle|file=no|paragraphs=1,2}}
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