title: Induction of labor and cesarean delivery by gestational age.
abstract: OBJECTIVE
  Studies of cesarean delivery (CD) rates among women undergoing induction of labor (IOL) often compare such women to women experiencing spontaneous labor at similar gestational ages. We sought to examine the association between IOL at various gestational ages and CD, accounting for the effect of increased gestational age among the comparison group who were managed expectantly.
  
  
  METHODS
  We conducted a retrospective cohort study of all term, singleton, cephalic presentation pregnancies delivered at our institution over 15 years excluding cesarean deliveries before labor. For each gestational age of induction, we created a comparison group of women who were undelivered at that gestational age, and who experienced labor at some future gestational age.
  
  
  RESULTS
  In women undergoing IOL at 38 weeks gestation, the CD rate was 11.9% as compared to 13.3% (P = .42) of women beyond 38 weeks gestation. The CD rate for induction of labor compared to ongoing pregnancy was 14.3% versus 15.0% (P = .62) at 39 weeks, 20.4% versus 19.0% (P = .41) at 40 weeks, and 24.3% versus 26.0% (P = .39) at 41 weeks. When controlling for potential confounding, there was a higher rate of CD among women with expectant management beyond 38 weeks (adjusted odds ratio [AOR] 1.80; 95% CI 1.29-2.53), 39 weeks (1.39; 95% CI 1.08-1.80), and 40 weeks (AOR 1.27; 95% CI 1.00-1.62).
  
  
  CONCLUSIONS
  Our findings suggest that IOL may not increase a woman's risk of CD when compared to expectant management. While this question has been addressed prospectively at 41 weeks gestation, it requires further examination at earlier gestations and among various subgroups.
authors.affiliation: Department of Obstetrics, Gynecology and Reproductive Sciences, University of California, San Francisco, San Francisco, CA, USA.
authors.forename: Aaron B
authors.initials: AB
authors.lastname: Caughey
authors.forename: James M
authors.initials: JM
authors.lastname: Nicholson
authors.forename: Yvonne W
authors.initials: YW
authors.lastname: Cheng
authors.forename: Deirdre J
authors.initials: DJ
authors.lastname: Lyell
authors.forename: A Eugene
authors.initials: AE
authors.lastname: Washington
mesh_terms: D002585:Cesarean Section / Q000706:statistics & numerical data*; D005260:Female; D005865:Gestational Age; D006801:Humans; D007751:Labor, Induced / Q000706:statistics & numerical data*; D015999:Multivariate Analysis; D016017:Odds Ratio; D010298:Parity; D011247:Pregnancy; D012189:Retrospective Studies