title: Cesarean delivery in the second stage of labor and the risk of subsequent premature birth.
abstract: Cesarean delivery is being increasingly used by obstetricians for indicated deliveries in the second stage of labor. Unplanned extension of the uterine incision involving the cervix often occurs with these surgeries. Therefore, we hypothesized that cesarean delivery in the second stage of labor may increase the rate of subsequent spontaneous premature birth.
  
  
  
  We sought to determine if cesarean delivery in the late first stage of labor or in the second stage of labor increases the risk of a subsequent spontaneous preterm birth.
  
  
  
  We conducted a retrospective cohort study of matched first and second births from a large Canadian perinatal database. The primary outcomes were spontaneous premature birth <37 and <32 weeks of gestation in the second birth. The exposure was stage of labor and cervical dilation at the time of the first cesarean delivery. The protocol and analysis plan was registered prior to obtaining data at Open Science Foundation.
  
  
  
  In total, 189,021 paired first and second births were identified. The risk of spontaneous preterm delivery <37 and <32 weeks of gestation in the second birth was increased when the first birth was by cesarean delivery in the second stage of labor (relative risk, 1.57; 95% confidence interval, 1.43-1.73 and relative risk, 2.12; 95% confidence interval, 1.67-2.68, respectively). The risk of perinatal death in the second birth, excluding congenital anomalies, was also correspondingly increased (relative risk, 1.44; 95% confidence interval, 1.05-1.96).
  
  
  
  Cesarean delivery in second stage of labor was associated with a 2-fold increase in the risk of spontaneous preterm birth <32 weeks of gestation in a subsequent birth. This information may inform management of operative delivery in the second stage.
authors.affiliation: Department of Obstetrics and Gynecology, University of Calgary, Calgary, Alberta, Canada; O'Brien Institute for Public Health, University of Calgary, Calgary, Alberta, Canada. Electronic address: Stephen.wood@albertahealthservices.ca.
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Wood
authors.affiliation: Department of Obstetrics and Gynecology, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Selphee
authors.initials: S
authors.lastname: Tang
authors.affiliation: Alberta Health Services, Edmonton, Alberta, Canada.
authors.forename: Susan
authors.initials: S
authors.lastname: Crawford
mesh_terms: D000293:Adolescent; D000328:Adult; D002170:Canada; D002585:Cesarean Section / Q000009:adverse effects*; D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D007748:Labor Stage, Second; D011247:Pregnancy; D047928:Premature Birth / Q000453:epidemiology*; D012189:Retrospective Studies; D012307:Risk Factors; D055815:Young Adult
keywords: cesarean delivery; preterm birth; second stage of labor