title: Normal labor: mechanism and duration.
abstract: Labor is refers to the chain of physiologic events that allows a fetus to undertake its journey from the uterus to the outside world. The mean duration of a singleton preganancy is 40.0 weeks (280 days), which is dated from the first day of the last normal menstrual period. The period from 37.0 weeks (259 days) to 42.0 weeks (294 days) of gestation is regarded as "term". This article focuses on the onset progress, and mechanics of normal labor term. Topics such as preterm labor (labor before 37 weeks), postterm labor (labor after 42 weeks), and abnormal labor and delivery have not been addressed and are discussed in detail elsewhere in this issue.
authors.affiliation: Division of Reproductive Sciences, Department of Obstetrics, Gynecology and Reproductive Sciences, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA.
authors.forename: John B
authors.initials: JB
authors.lastname: Liao
authors.forename: Catalin S
authors.initials: CS
authors.lastname: Buhimschi
authors.forename: Errol R
authors.initials: ER
authors.lastname: Norwitz
mesh_terms: D005260:Female; D006801:Humans; D007747:Labor Stage, First / Q000502:physiology; D007748:Labor Stage, Second / Q000502:physiology; D007749:Labor Stage, Third / Q000502:physiology; D007743:Labor, Obstetric / Q000502:physiology*; D011247:Pregnancy / Q000502:physiology