Editing Cervix (section)

=== 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>