Editing Childbirth (section)

===Onset of labour===
[[File:2919 Hormones Initiating Labor-02.jpg|thumb|upright=1.3|The hormones initiating labour]]
Definitions of the onset of labour include:
* Regular uterine contractions at least every six minutes with evidence of change in [[cervical dilation]] or [[cervical effacement]] between consecutive digital examinations.<ref>{{cite journal | vauthors = Kupferminc M, Lessing JB, Yaron Y, Peyser MR | title = Nifedipine versus ritodrine for suppression of preterm labour | journal = British Journal of Obstetrics and Gynaecology | volume = 100 | issue = 12 | pages = 1090–94 | date = December 1993 | pmid = 8297841 | doi = 10.1111/j.1471-0528.1993.tb15171.x | s2cid = 24521943 }}</ref>
* Regular contractions occurring less than 10 minutes apart and progressive cervical dilation or cervical effacement.<ref>{{cite journal | vauthors = Jokic M, Guillois B, Cauquelin B, Giroux JD, Bessis JL, Morello R, Levy G, Ballet JJ | title = Fetal distress increases interleukin-6 and interleukin-8 and decreases tumour necrosis factor-alpha cord blood levels in noninfected full-term neonates | journal = BJOG | volume = 107 | issue = 3 | pages = 420–25 | date = March 2000 | pmid = 10740342 | doi = 10.1111/j.1471-0528.2000.tb13241.x | doi-access = free }}</ref>
* At least three painful regular uterine contractions during a 10-minute period, each lasting more than 45 seconds.<ref>{{cite journal | vauthors = Lyrenäs S, Clason I, Ulmsten U | title = In vivo controlled release of PGE2 from a vaginal insert (0.8 mm, 10 mg) during induction of labour | journal = BJOG | volume = 108 | issue = 2 | pages = 169–78 | date = February 2001 | pmid = 11236117 | doi = 10.1111/j.1471-0528.2001.00039.x | s2cid = 45247771 }}</ref>

Common signs that labour is about to begin may include what is known as ''lightening'', which is the process of the baby moving down from the rib cage with the head of the baby engaging deep in the pelvis. The pregnant woman may then find breathing easier, since her lungs have more room for expansion, but pressure on her bladder may cause more frequent need to urinate. Lightening may occur a few weeks or a few hours before labour begins, or even not until labour has begun.<ref name="mayoclinic.org">{{cite web|title=Labor and delivery, postpartum care|url=https://www.mayoclinic.org/healthy-lifestyle/labor-and-delivery/in-depth/signs-of-labor/art-20046184|website=Mayo Clinic|access-date=7 May 2018|archive-date=7 May 2018|archive-url=https://web.archive.org/web/20180507222539/https://www.mayoclinic.org/healthy-lifestyle/labor-and-delivery/in-depth/signs-of-labor/art-20046184|url-status=live}}</ref> Some women also experience an increase in vaginal discharge several days before labour begins when the "[[Cervical mucus plug|mucus plug]]", a thick plug of [[mucus]] that blocks the opening to the uterus, is pushed out into the vagina.  The mucus plug may become dislodged days before labour begins or not until the start of labour.<ref name="mayoclinic.org"/>

While inside the uterus the baby is enclosed in a fluid-filled membrane called the [[amniotic sac]].  Shortly before, at the beginning of, or during labour the [[rupture of membranes|sac ruptures]], commonly known as the "water breaking". Once the sac ruptures the baby is at risk for infection and the mother's medical team will assess the need to [[Labor induction|induce labour]] if it has not started within the time they believe to be safe for the infant.<ref name="mayoclinic.org"/>