title: Does stage of labor at time of cesarean delivery affect risk of subsequent preterm birth?
abstract: OBJECTIVE
  The effect of a cesarean delivery in different stages of labor on spontaneous preterm birth (sPTB) in a subsequent pregnancy has not been studied extensively. The objective of the study was to evaluate the risk of subsequent sPTB after a first-stage or second-stage cesarean delivery compared with a vaginal delivery.
  
  
  METHODS
  This was a planned secondary analysis of a large retrospective cohort study of women with 2 consecutive deliveries from 2005-2010. Women with a previous sPTB were excluded. First-stage (<10 cm) and second-stage (≥10 cm) cesarean deliveries were compared with vaginal deliveries. Data were obtained through chart abstraction. The primary outcome was sPTB (<37 wk) in a subsequent pregnancy. Categoric variables were compared with the use of χ(2) analyses, and logistic regression was used to calculate odds and control for confounders.
  
  
  RESULTS
  Eight hundred eighty-seven women were included (721 vaginal deliveries; 129 first-stage and 37 second-stage cesarean deliveries). The sPTB rate varied between groups (7.8%, 2.3%, and 13.5%, respectively; P = .03). When compared with women with a vaginal delivery, women with a first-stage cesarean delivery had a decreased risk of sPTB, which remained after adjustment for confounders (adjusted odds ratio, 0.30; 95% confidence interval, 0.09-0.99; P = .049). There was a nonsignificant increase in odds of sPTB after a second-stage cesarean delivery compared with a vaginal delivery (adjusted odds ratio, 2.4; 95% confidence interval, 0.77-7.43; P = .13). Women with a second-stage cesarean delivery had a 6-fold higher odds of sPTB compared with women with a first-stage cesarean delivery, which remained after adjustment for confounders (adjusted odds ratio, 5.8; 95% confidence interval, 1.08-30.8; P = .04).
  
  
  CONCLUSIONS
  Women with a full-term second-stage cesarean delivery have a significantly higher than expected rate of subsequent sPTB (13.5%) compared with both the overall national sPTB rate (7-8%) and to a first-stage cesarean delivery (2.3%). As the cesarean delivery rate continues to rise, this potential impact on pregnancy outcomes cannot be ignored.
authors.affiliation: Maternal and Child Health Research Department, Department of Obstetrics and Gynecology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA. Electronic address: lisa.obgyndoc@gmail.com.
authors.forename: Lisa D
authors.initials: LD
authors.lastname: Levine
authors.affiliation: Department of Biostatistics and Epidemiology, Center for Clinical Epidemiology and Biostatistics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA.
authors.forename: Mary D
authors.initials: MD
authors.lastname: Sammel
authors.affiliation: Maternal and Child Health Research Department, Department of Obstetrics and Gynecology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA.
authors.forename: Adi
authors.initials: A
authors.lastname: Hirshberg
authors.affiliation: Maternal and Child Health Research Department, Department of Obstetrics and Gynecology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA.
authors.forename: Michal A
authors.initials: MA
authors.lastname: Elovitz
authors.affiliation: Maternal and Child Health Research Department, Department of Obstetrics and Gynecology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA.
authors.forename: Sindhu K
authors.initials: SK
authors.lastname: Srinivas
mesh_terms: D000293:Adolescent; D000328:Adult; D002585:Cesarean Section / Q000379:methods*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007747:Labor Stage, First; D007748:Labor Stage, Second; D016015:Logistic Models; D011183:Postoperative Complications / Q000209:etiology*; D011247:Pregnancy; D047928:Premature Birth / Q000209:etiology*; D012189:Retrospective Studies; D012307:Risk Factors; D055815:Young Adult
keywords: cesarean delivery; preterm birth; second stage of labor