title: The effect of labour induction on the risk of caesarean delivery: using propensity scores to control confounding by indication.
abstract: OBJECTIVE
  To use propensity score methods to control for confounding by indication in the association between labour induction and caesarean delivery.
  
  
  METHODS
  Cross-sectional analysis of administrative hospital discharge data supplemented by medical record information.
  
  
  METHODS
  Fourteen US member hospitals of the National Perinatal Information Center.
  
  
  METHODS
  A cohort of 166 559 singleton liveborn deliveries in the period 2007-2012.
  
  
  METHODS
  We used propensity scores (PSs) to balance 83 covariates between induced and non-induced women, and compared estimates with traditional covariate adjustment. We estimated PSs for labour induction versus expectant management of pregnancy each week from 34 to 42 weeks of gestation. We estimated risk ratios (RRs) for the association between labour induction and primary caesarean delivery from models with no adjustment, traditional adjustment of five covariates, matched PS, and adjustment for continuous PS.
  
  
  METHODS
  Caesarean delivery in current or subsequent week of gestation.
  
  
  RESULTS
  In crude models labour induction increased the risk of caesarean delivery in all weeks (RR 1.06-1.52), excepting 39 weeks of gestation (RR 0.89). After matching on PS, the analysis showed a significantly decreased risk of caesarean delivery with labour induction during weeks 35-39 (RR 0.77-0.92), and a significantly elevated risk at weeks 40 (RR 1.22) and 41 (RR 1.39). Traditional covariate and PS adjustment resulted in RRs between those from crude and PS-matched models.
  
  
  CONCLUSIONS
  There is evidence of considerable confounding by indication in the association of labour induction and caesarean delivery, particularly for preterm deliveries. Using PS methods, we found a reduced risk of caesarean delivery with labour induction before 40 weeks of gestation, and an elevated risk for weeks 40-42.
  
  
  CONCLUSIONS
  With confounding adjustment, labour induction does not increase the risk of caesarean at 34-39 weeks of gestation.
authors.affiliation: Department of Epidemiology, Brown University School of Public Health, Providence, RI, USA.|Division of Research, Department of Obstetrics and Gynecology, Women and Infants Hospital, Providence, RI, USA.
authors.forename: V A
authors.initials: VA
authors.lastname: Danilack
authors.affiliation: Department of Health Services, Policy, and Practice, Brown University School of Public Health, Providence, RI, USA.|Optum Epidemiology, Waltham, MA, USA.
authors.forename: D D
authors.initials: DD
authors.lastname: Dore
authors.affiliation: Department of Epidemiology, Brown University School of Public Health, Providence, RI, USA.
authors.forename: E W
authors.initials: EW
authors.lastname: Triche
authors.affiliation: National Perinatal Information Center/Quality Analytic Services, Inc., Providence, RI, USA.
authors.forename: J H
authors.initials: JH
authors.lastname: Muri
authors.affiliation: Division of Research, Department of Obstetrics and Gynecology, Women and Infants Hospital, Providence, RI, USA.|Department of Obstetrics and Gynecology, Warren Alpert Medical School of Brown University, Providence, RI, USA.
authors.forename: M G
authors.initials: MG
authors.lastname: Phipps
authors.affiliation: Department of Epidemiology, Brown University School of Public Health, Providence, RI, USA.|Department of Obstetrics and Gynecology, Warren Alpert Medical School of Brown University, Providence, RI, USA.
authors.forename: D A
authors.initials: DA
authors.lastname: Savitz
mesh_terms: D000328:Adult; D002585:Cesarean Section / Q000706:statistics & numerical data*; D015331:Cohort Studies; D015986:Confounding Factors, Epidemiologic; D003430:Cross-Sectional Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D007751:Labor, Induced / Q000706:statistics & numerical data*; D011247:Pregnancy; D057216:Propensity Score; D012306:Risk; D014481:United States
keywords: Caesarean section; confounding variables; induced labour; obstetric delivery; pregnancy; propensity score