Editing Cervix (section)

== Function ==
=== Fertility ===
The cervical canal is a pathway through which sperm enter the uterus after being induced by [[estradiol]] after [[penile-vaginal intercourse]],<ref name=GUYTONHALL2005>{{cite book| vauthors = Guyton AC, Hall JE |title=Textbook of Medical Physiology|date=2005|publisher=W.B. Saunders|location=Philadelphia, PA|isbn=978-0-7216-0240-0|page=1027|edition=11th}}</ref> and some forms of [[artificial insemination]].<ref>{{cite web|title=Demystifying IUI, ICI, IVI and IVF |date=4 January 2014 |url=https://www.seattlespermbank.com/demystifying-iui-ici-ivi-and-ivf/ |publisher=Seattle Sperm Bank |access-date=9 November 2014}}</ref> Some sperm remains in cervical crypts, infoldings of the endocervix, which act as a reservoir, releasing sperm over several hours and maximising the chances of fertilisation.<ref name=BRANNIGAN2008>{{cite journal| vauthors = Brannigan RE, Lipshultz LI |title=Sperm Transport and Capacitation|year=2008|journal=The Global Library of Women's Medicine|doi=10.3843/GLOWM.10316|url=http://www.glowm.com/section_view/heading/Sperm%20Transport%20and%20Capacitation/item/315}}</ref> A theory states the cervical and uterine contractions during [[orgasm]] draw semen into the uterus.<ref name=GUYTONHALL2005 /> Although the "upsuck theory" has been generally accepted for some years, it has been disputed due to lack of evidence, small sample size, and methodological errors.<ref>{{cite journal| vauthors = Levin RJ |title=The human female orgasm: a critical evaluation of its proposed reproductive functions|journal=Sexual and Relationship Therapy|date=November 2011|volume=26|issue=4|pages=301–14|doi=10.1080/14681994.2011.649692|s2cid=143550619}}</ref><ref>{{cite journal | vauthors = Borrow AP, Cameron NM | title = The role of oxytocin in mating and pregnancy | journal = Hormones and Behavior | volume = 61 | issue = 3 | pages = 266–276 | date = March 2012 | pmid = 22107910 | doi = 10.1016/j.yhbeh.2011.11.001 | s2cid = 45783934 }}</ref>

Some methods of [[fertility awareness]], such as the [[Creighton Model FertilityCare System|Creighton model]] and the [[Billings ovulation method|Billings method]] involve estimating a woman's periods of fertility and infertility by observing physiological changes in her body.<ref>{{Cite journal |last=Thijssen |first=A. |last2=Meier |first2=A. |last3=Panis |first3=K. |last4=Ombelet |first4=W. |date=2014 |title='Fertility Awareness-Based Methods' and subfertility: a systematic review |url=https://pubmed.ncbi.nlm.nih.gov/25374654 |journal=Facts, Views & Vision in ObGyn |volume=6 |issue=3 |pages=113–123 |issn=2032-0418 |pmc=4216977 |pmid=25374654}}</ref> Among these changes are several involving the quality of her cervical mucus: the sensation it causes at the [[vulva]], its elasticity (''[[Spinnbarkeit]]''), its transparency, and the presence of [[Fern test|ferning]].<ref name="Weschler"/>

=== Cervical mucus ===
Several hundred glands in the endocervix produce 20–60&nbsp;mg of cervical [[mucus]] a day, increasing to 600&nbsp;mg around the time of ovulation. It is viscous because it contains large proteins known as [[mucin]]s. The viscosity and water content vary during the [[menstrual cycle]]; mucus is composed of around 93% water, reaching 98% at midcycle. These changes allow it to function as a barrier or a transport medium to spermatozoa. It contains electrolytes such as calcium, sodium, and potassium; organic components such as glucose, amino acids, and soluble proteins; trace elements including zinc, copper, iron, manganese, and selenium; free fatty acids; enzymes such as [[amylase]]; and [[prostaglandins]].<ref name=CERVIX2006>{{cite book| vauthors = Sharif K, Olufowobi O |title=The Cervix|url=https://archive.org/details/cervixndedition00jord|url-access=limited| veditors = Jordan J, Singer A, Jones H, Shafi M |publisher=Blackwell Publishing|location=Malden, MA | date=2006|edition=2nd|pages=[https://archive.org/details/cervixndedition00jord/page/n171 157]–68 |chapter=The structure chemistry and physics of human cervical mucus|isbn=978-1-4051-3137-7}}</ref><!-- cites four previous sentences --> Its consistency is determined by the influence of the hormones estrogen and progesterone. At midcycle, around the time of [[ovulation]]—a period of high estrogen levels— the mucus is thin and serous to allow sperm to enter the uterus and is more alkaline and, hence, more hospitable to sperm.<ref name=BRANNIGAN2008 /> It is also higher in electrolytes, which results in the "ferning" pattern that can be observed in drying mucus under low magnification; as the mucus dries, the salts crystallize, resembling the leaves of a fern.<ref name = Weschler/> The mucus has a stretchy character described as ''Spinnbarkeit'' most prominent around ovulation.<ref name="pmid15775876">{{cite journal | vauthors = Anderson M, Karasz A, Friedland S | title = Are vaginal symptoms ever normal? a review of the literature | journal = MedGenMed | volume = 6 | issue = 4 | pages = 49 | date = November 2004 | pmid = 15775876 | pmc = 1480553 }}</ref>

At other times in the cycle, the mucus is thick and more acidic due to the effects of progesterone.<ref name=BRANNIGAN2008 /> This "infertile" mucus acts as a barrier to keep sperm from entering the uterus.<ref>{{cite book | vauthors = Westinore A, Billings E |title=The Billings Method: Controlling Fertility Without Drugs or Devices |publisher=Life Cycle Books |location=Toronto, ON |year=1998 |page=37 |isbn=0-919225-17-9}}</ref> Women taking an [[oral contraceptive pill]] also have thick mucus from the effects of progesterone.<ref name=BRANNIGAN2008 /> Thick mucus also prevents [[pathogen]]s from interfering with a nascent pregnancy.<ref name="pmid7431318">{{cite journal | vauthors = Wagner G, Levin RJ | title = Electrolytes in vaginal fluid during the menstrual cycle of coitally active and inactive women | journal = Journal of Reproduction and Fertility | volume = 60 | issue = 1 | pages = 17–27 | date = September 1980 | pmid = 7431318 | doi = 10.1530/jrf.0.0600017 | doi-access = free }}</ref>

A [[cervical mucus plug]], called the operculum, forms inside the cervical canal during pregnancy. This provides a protective seal for the uterus against the entry of pathogens and leakage of uterine fluids. The mucus plug is also known to have antibacterial properties. This plug is released as the cervix dilates, either during the first stage of childbirth or shortly before.<ref>{{cite journal | vauthors = Becher N, Adams Waldorf K, Hein M, Uldbjerg N | title = The cervical mucus plug: structured review of the literature | journal = Acta Obstetricia et Gynecologica Scandinavica | volume = 88 | issue = 5 | pages = 502–513 | date = May 2009 | pmid = 19330570 | doi = 10.1080/00016340902852898 | s2cid = 23738950 }}</ref> It is visible as a blood-tinged mucous discharge.<ref>{{cite book| vauthors =  Lowdermilk DL, Perry SE |title=Maternity Nursing|year=2006|publisher=Elsevier Mosby|location=Edinburgh, United Kingdom|isbn=978-0-323-03366-4|page=[https://archive.org/details/maternitynursing00deit/page/394 394]|edition=7th|url=https://archive.org/details/maternitynursing00deit/page/394}}</ref>

=== Childbirth ===
[[File:Positive Feedback- Childbirth (1).svg|thumb|upright=0.6|When the head of the fetus pushes against the cervix, a signal (2) is sent to the brain. This causes a signal to be sent to the [[pituitary gland]] to release oxytocin (4). Oxytocin is carried in the bloodstream to the uterus, causing contractions to induce childbirth.]]

The cervix plays a major role in [[childbirth]]. As the [[fetus]] descends within the uterus in preparation for birth, the [[Presentation (obstetrics)|presenting part]], usually [[cephalic presentation|the head]], rests on and is supported by the cervix.<ref name=WILLIAMS2005/> As labour progresses, the cervix becomes softer and shorter, begins to dilate, and withdraws to face the anterior of the body.<ref name=GOLDENBERG2008 /> The support the cervix provides to the fetal head starts to give way when the uterus begins its [[Uterine contraction|contractions]]. During childbirth, the [[Cervical dilation|cervix must dilate]] to a diameter of more than {{convert|abbr=on|10|cm|in|1}} to accommodate the head of the fetus as it descends from the uterus to the vagina. In becoming wider, the cervix also becomes shorter, a phenomenon known as [[cervical effacement|effacement]].<ref name=WILLIAMS2005 />

Along with other factors, midwives and doctors use the extent of [[cervical dilation]] to assist decision-making during [[Stages of labor|childbirth]].<ref name=NICE-labour>NICE (2007). Section 1.6, ''Normal labour: first stage''</ref><ref name="NICE 2007">NICE (2007). Section 1.7, ''Normal labour: second stage''</ref> Generally, the active first stage of labour, when the uterine contractions become strong and regular,<ref name=NICE-labour/> begins when the cervical dilation is more than {{convert|3–5|cm|in|abbr=on}}.<ref>{{cite news|author=ACOG|title=Obstetric Data Definitions Issues and Rationale for Change|url=http://www.acog.org/About_ACOG/ACOG_Departments/Patient_Safety_and_Quality_Improvement/~/media/Departments/Patient%20Safety%20and%20Quality%20Improvement/201213IssuesandRationale-Labor.pdf|year=2012|work=Revitalize|access-date=4 November 2014|url-status=dead|archive-url=https://web.archive.org/web/20131106064308/http://www.acog.org/About_ACOG/ACOG_Departments/Patient_Safety_and_Quality_Improvement/~/media/Departments/Patient%20Safety%20and%20Quality%20Improvement/201213IssuesandRationale-Labor.pdf|archive-date=6 November 2013|author-link=American Congress of Obstetricians and Gynecologists}}</ref><ref>{{cite journal | vauthors = Su M, Hannah WJ, Willan A, Ross S, Hannah ME | title = Planned caesarean section decreases the risk of adverse perinatal outcome due to both labour and delivery complications in the Term Breech Trial | journal = BJOG | volume = 111 | issue = 10 | pages = 1065–1074 | date = October 2004 | pmid = 15383108 | doi = 10.1111/j.1471-0528.2004.00266.x | s2cid = 10086313 | doi-access =  }}</ref> The second phase of labor begins when the cervix has dilated to {{convert|10|cm|in|sigfig=1|abbr=on}}, which is regarded as its fullest dilation,<ref name=WILLIAMS2005>{{cite book| vauthors = Cunningham F, Leveno K, Bloom S, Hauth J, Gilstrap L, Wenstrom K |title=Williams obstetrics |year=2005|publisher=McGraw-Hill Professional|location=New York; Toronto |isbn=0-07-141315-4|edition=22nd|pages=157–60, 537–39}}</ref> and is when active pushing and contractions push the baby along the [[birth canal]] leading to the birth of the baby.<ref name="NICE 2007"/> [[parity (biology)|The number of past vaginal deliveries]] is a strong factor in influencing how rapidly the cervix can dilate in labour.<ref name="WILLIAMS2005" /> The time taken for the cervix to dilate and efface is one factor used in reporting systems such as the [[Bishop score]], used to recommend whether interventions such as a [[forceps delivery]], [[Labor induction|induction]], or [[Caesarean section]] should be used in childbirth.<ref name="WILLIAMS2005" />

[[Cervical incompetence]] is a condition in which shortening of the cervix due to dilation and thinning occurs before term pregnancy. Short cervical length is the strongest predictor of [[preterm birth]].<ref name=GOLDENBERG2008>{{cite journal | vauthors = Goldenberg RL, Culhane JF, Iams JD, Romero R | title = Epidemiology and causes of preterm birth | journal = Lancet | volume = 371 | issue = 9606 | pages = 75–84 | date = January 2008 | pmid = 18177778 | pmc = 7134569 | doi = 10.1016/S0140-6736(08)60074-4 }}</ref>

=== Contraception ===
Several methods of [[contraception]] involve the cervix. [[Diaphragm (contraceptive)|Cervical diaphragm]]s are reusable, firm-rimmed plastic devices inserted by a woman before intercourse that cover the cervix. Pressure against the walls of the vagina maintain the position of the diaphragm, and it acts as a physical barrier to prevent the entry of sperm into the uterus, preventing [[fertilisation]]. [[Cervical cap]]s are a similar method, although they are smaller and adhere to the cervix by suction. Diaphragms and caps are often used in conjunction with [[spermicide]]s.<ref>{{cite book | author = NSW Family Planning|title=Contraception: healthy choices: a contraceptive clinic in a book|year=2009|publisher=UNSW Press|location=Sydney, New South Wales|isbn=978-1-74223-136-5|pages=27–37|edition=2nd}}</ref> In one year, 12% of women using the diaphragm will undergo an unintended pregnancy, and with optimal use this falls to 6%.<ref>{{cite journal | vauthors = Trussell J | title = Contraceptive failure in the United States | journal = Contraception | volume = 83 | issue = 5 | pages = 397–404 | date = May 2011 | pmid = 21477680 | pmc = 3638209 | doi = 10.1016/j.contraception.2011.01.021 }}</ref> Efficacy rates are lower for the cap, with 18% of women undergoing an unintended pregnancy, and 10–13% with optimal use.<ref>{{cite journal | vauthors = Trussell J, Strickler J, Vaughan B | title = Contraceptive efficacy of the diaphragm, the sponge and the cervical cap | journal = Family Planning Perspectives | volume = 25 | issue = 3 | pages = 100–5, 135 | date = May–Jun 1993 | pmid = 8354373 | doi = 10.2307/2136156 | jstor = 2136156 }}</ref> Most types of [[progestogen-only pill]]s are effective as a contraceptive because they thicken cervical mucus, making it difficult for sperm to pass along the cervical canal.<ref name=FPA-POP>{{cite book|title=Your Guide to the progesterone-one pill |url=http://www.fpa.org.uk/sites/default/files/progestogen-only-pill-your-guide.pdf |archive-url=https://web.archive.org/web/20140327100545/http://www.fpa.org.uk/sites/default/files/progestogen-only-pill-your-guide.pdf |archive-date=2014-03-27 |url-status=live |publisher=Family Planning Association (UK)|access-date=9 November 2014 |pages=3–4 |isbn=978-1-908249-53-1}}</ref> In addition, they may also sometimes prevent ovulation.<ref name=FPA-POP/> In contrast, contraceptive pills that contain both oestrogen and progesterone, the [[combined oral contraceptive pill]]s, work mainly by preventing [[ovulation]].<ref name=FPA-COC/> They also thicken cervical mucus and thin the lining of the uterus, enhancing their effectiveness.<ref name=FPA-COC>{{cite book|title=Your Guide to the combined pill |url=http://www.fpa.org.uk/sites/default/files/the-combined-pill-your-guide.pdf |archive-url=https://web.archive.org/web/20131102201353/http://www.fpa.org.uk/sites/default/files/the-combined-pill-your-guide.pdf |archive-date=2013-11-02 |url-status=live |publisher=Family Planning Association (UK) |access-date=9 November 2014 |page=4 |date =January 2014 |isbn=978-1-908249-50-0}}</ref>