title: Term induction of labor and subsequent preterm birth.
abstract: OBJECTIVE
  Although the rate of inductions continues to rise, there is a paucity of data investigating subsequent pregnancy outcomes after induction. Our objective was to compare term inductions with term spontaneous labor and evaluate the rate of subsequent spontaneous preterm birth (sPTB).
  
  
  METHODS
  A retrospective cohort study of women with 2 consecutive deliveries from 2005 through 2010 was performed. Term inductions or term spontaneous labor in the index pregnancy was included, and those with a prior sPTB were excluded. Data were obtained through chart abstraction. The primary outcome was sPTB (<37 weeks) in a subsequent pregnancy. Categorical variables were compared with χ(2) analyses, and logistic regression was used to calculate odds.
  
  
  RESULTS
  Eight hundred eighty-seven women were included (622 inductions, 265 spontaneous labor). The overall subsequent sPTB rate was 7.2%. Term inductions were less likely to have a subsequent sPTB compared with term spontaneous labor (6% vs 11%; odds ratio [OR], 0.49; 95% confidence interval, 0.29-0.81; P = .005). This remained after adjusting for confounders (adjusted OR, 0.55; P = .04). The sPTB risk depended on gestational age of index delivery. At 37-38.9 weeks, the sPTB rate after spontaneous labor was 24% vs 9% after induction (OR, 3.0; 95% confidence interval, 1.44-6.16; P = .003). This was not significant for 39-39.9 weeks (P = .2) or 40 weeks or longer (P = .8).
  
  
  CONCLUSIONS
  Induction is not a risk factor for subsequent sPTB. Spontaneous labor, however, in the early term period is associated with subsequent sPTB. Further investigation among early term deliveries is warranted to evaluate the risk of sPTB and target interventions in this cohort.
authors.affiliation: 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 Family Medicine and Community Health, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA.
authors.forename: Hillary R
authors.initials: HR
authors.lastname: Bogner
authors.affiliation: 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: 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: 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: 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: D000328:Adult; D002585:Cesarean Section / Q000706:statistics & numerical data; D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D007363:Intensive Care Units, Neonatal; D007751:Labor, Induced / Q000379:methods / Q000706:statistics & numerical data*; D007752:Obstetric Labor, Premature / Q000453:epidemiology*; D010343:Patient Admission / Q000706:statistics & numerical data; D006473:Postpartum Hemorrhage / Q000453:epidemiology; D011247:Pregnancy; D047928:Premature Birth / Q000453:epidemiology*; D012189:Retrospective Studies; D047929:Term Birth; D055815:Young Adult
keywords: induction of labor; spontaneous early term labor; subsequent preterm birth