title: The natural history of the normal first stage of labor.
authors.forename: Ariel L
authors.initials: AL
authors.lastname: Zimerman
authors.forename: Ana
authors.initials: A
authors.lastname: Smolin
mesh_terms: D002584:Cervix Uteri / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D007747:Labor Stage, First / Q000502:physiology*; D011247:Pregnancy; D014463:Ultrasonography