title: Comparing expectant management and spontaneous labor approaches in studying the effect of labor induction on cesarean delivery.
abstract: Evidence of the impact of labor induction on cesarean delivery (CD) remains inconclusive because of differing methodological approaches. A spontaneous labor comparison group describes patterns retrospectively, whereas an expectant management comparison group prospectively evaluates a decision to induce. We examined the influence of comparison group on the association between labor induction and CD.
  
  
  
  We studied 166,559 mother-newborn dyads from 14 National Perinatal Information Center member hospitals, 2007-2012. We included singleton births 34-42 completed weeks' gestation and excluded women with contraindications to vaginal delivery. We calculated risk ratios (RR) adjusted for hypertensive and diabetic disorders, intrauterine growth restriction, parity, and maternal age.
  
  
  
  When comparing induction to spontaneous labor, induction had significantly lower risk for CD at weeks 34-35 (adjusted RR [95% confidence interval (CI)]: 0.6 [0.5, 0.7] for week 34 and 0.7 [0.6, 0.8] for week 35) and higher risk at weeks 37-41 (adjusted RRs [95% CIs]: 1.8 [1.6, 2.1], 2.1 [1.9, 2.2], 1.8 [1.7, 1.9], 1.9 [1.8, 2.0], and 1.6 [1.5, 1.7], respectively). When comparing induction to expectant management, adjusted RRs [95% CIs] were significantly below 1.0 for week 34 (0.8 [0.7, 0.9]), week 36 (0.9 [0.8, 0.9]), and week 37 (0.9 [0.8, 0.9]), and were only elevated at week 40 (1.4 [1.3, 1.4]) and week 41 (1.4 [1.3, 1.5]).
  
  
  
  Using two different methodological approaches with the same sample, we confirm that comparing labor induction to spontaneous onset of labor, instead of expectant management of pregnancy, does not fully inform clinical practice and may lead to an exaggerated estimate of the risk of CD.
authors.affiliation: Department of Epidemiology, Brown University School of Public Health, Providence, RI; Division of Research, Department of Obstetrics and Gynecology, Women & Infants Hospital, Providence, RI. Electronic address: vdanilack@wihri.org.
authors.forename: Valery A
authors.initials: VA
authors.lastname: Danilack
authors.affiliation: Department of Epidemiology, Brown University School of Public Health, Providence, RI.
authors.forename: Elizabeth W
authors.initials: EW
authors.lastname: Triche
authors.affiliation: Department of Health Services, Policy, and Practice, Brown University School of Public Health, Providence, RI; Optum Epidemiology, Waltham, MA.
authors.forename: David D
authors.initials: DD
authors.lastname: Dore
authors.affiliation: National Perinatal Information Center/Quality Analytic Services, Inc., Providence, RI.
authors.forename: Janet H
authors.initials: JH
authors.lastname: Muri
authors.affiliation: Department of Epidemiology, Brown University School of Public Health, Providence, RI; Division of Research, Department of Obstetrics and Gynecology, Women & Infants Hospital, Providence, RI; Department of Obstetrics and Gynecology, Warren Alpert Medical School of Brown University, Providence, RI.
authors.forename: Maureen G
authors.initials: MG
authors.lastname: Phipps
authors.affiliation: Department of Epidemiology, Brown University School of Public Health, Providence, RI; Department of Obstetrics and Gynecology, Warren Alpert Medical School of Brown University, Providence, RI.
authors.forename: David A
authors.initials: DA
authors.lastname: Savitz
mesh_terms: D000328:Adult; D002585:Cesarean Section / Q000379:methods / Q000706:statistics & numerical data*; D015331:Cohort Studies; D016208:Databases, Factual; D036861:Delivery, Obstetric / Q000379:methods; D005260:Female; D005865:Gestational Age; D006801:Humans; D015994:Incidence; D000068104:Infant Health; D007231:Infant, Newborn; D007745:Labor Onset / Q000502:physiology*; D007751:Labor, Induced / Q000379:methods / Q000706:statistics & numerical data*; D008423:Maternal Age; D010298:Parity; D011247:Pregnancy; D011248:Pregnancy Complications / Q000175:diagnosis / Q000453:epidemiology*; D011256:Pregnancy Outcome; D012189:Retrospective Studies; D018570:Risk Assessment; D055815:Young Adult
keywords: Cesarean section; Induced labor; Obstetric delivery; Pregnancy