title: The association between obstetrical interventions and late preterm birth.
abstract: OBJECTIVE
  There is concern that obstetric interventions (prelabor cesarean section and induced delivery) are drivers of late preterm (LP) birth. Our objective was to evaluate the independent association between obstetric interventions and LP birth and explore associated independent maternal and fetal risk factors for LP birth.
  
  
  METHODS
  In this population-based cross-sectional study, the BORN Information System was used to identify all infants born between 34 and 40 completed weeks of gestation between 2005 and 2012 in Ontario, Canada. The association between obstetric interventions (preterm cesarean section and induced delivery) and LP birth (34 to 36 completed weeks' gestation vs 37 to 40 completed weeks' gestation) was assessed using generalized estimating equation regression.
  
  
  RESULTS
  Of 917,013 births between 34 and 40 weeks, 49,157 were LP (5.4%). In the adjusted analysis, "any obstetric intervention" (risk ratio [RR], 0.65; 95% confidence interval [CI], 0.57-0.74), induction (RR, 0.71; 95% CI, 0.61-0.82) and prelabor cesarean section (RR, 0.66; 95% CI, 0.59-0.74) were all associated with a lower likelihood of LP vs term birth. Several independent potentially modifiable risk factors for LP birth were identified including previous cesarean section (RR, 1.28; 95% CI, 1.16-1.40), smoking during pregnancy (RR, 1.28; 95% CI, 1.21-1.36) and high material (RR, 1.1; 95% CI, 1.03-1.18) and social (RR, 1.09; 95% CI, 1.02-1.16) deprivation indices.
  
  
  CONCLUSIONS
  After accounting for differences in maternal and fetal risk, LP births had a 35% lower likelihood of obstetric interventions than term births. Obstetric care providers may be preferentially avoiding induction and prelabor cesarean section between 34 and 37 weeks' gestation.
authors.affiliation: Maternal-Infant Care Research Institute, Mount Sinai Hospital, Toronto, ON, Canada.
authors.forename: Kate L
authors.initials: KL
authors.lastname: Bassil
authors.affiliation: BORN Ontario (Better Outcomes Registry & Network), Ottawa, ON, Canada; Department of Obstetrics and Gynecology, Ottawa Hospital Research Institute, and Department of Epidemiology and Community Medicine, University of Ottawa, Ottawa, ON, Canada.
authors.forename: Abdool S
authors.initials: AS
authors.lastname: Yasseen
authors.affiliation: BORN Ontario (Better Outcomes Registry & Network), Ottawa, ON, Canada; Department of Obstetrics and Gynecology, Ottawa Hospital Research Institute, and Department of Epidemiology and Community Medicine, University of Ottawa, Ottawa, ON, Canada.
authors.forename: Mark
authors.initials: M
authors.lastname: Walker
authors.affiliation: Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, ON, Canada; Department of Pediatrics, St. Michael's Hospital, Toronto, ON, Canada; Department of Pediatrics, Faculty of Medicine, University of Toronto, Toronto, ON, Canada.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Sgro
authors.affiliation: Maternal-Infant Care Research Institute, Mount Sinai Hospital, Toronto, ON, Canada; Department of Pediatrics, Mount Sinai Hospital, Toronto, ON, Canada; Department of Pediatrics, Faculty of Medicine, University of Toronto, Toronto, ON, Canada.
authors.forename: Prakesh S
authors.initials: PS
authors.lastname: Shah
authors.affiliation: Department of Obstetrics and Gynecology, Faculty of Medicine, Queen's University, Kingston, ON, Canada.
authors.forename: Graeme N
authors.initials: GN
authors.lastname: Smith
authors.affiliation: Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, ON, Canada; Department of Pediatrics, St. Michael's Hospital, Toronto, ON, Canada.
authors.forename: Douglas M
authors.initials: DM
authors.lastname: Campbell
authors.affiliation: Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, ON, Canada; Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, ON, Canada.
authors.forename: Muhammad
authors.initials: M
authors.lastname: Mamdani
authors.affiliation: BORN Ontario (Better Outcomes Registry & Network), Ottawa, ON, Canada.
authors.forename: Ann E
authors.initials: AE
authors.lastname: Sprague
authors.affiliation: Maternal-Infant Care Research Institute, Mount Sinai Hospital, Toronto, ON, Canada; Department of Pediatrics, Mount Sinai Hospital, Toronto, ON, Canada; Department of Pediatrics, Faculty of Medicine, University of Toronto, Toronto, ON, Canada.
authors.forename: Shoo K
authors.initials: SK
authors.lastname: Lee
authors.affiliation: Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, ON, Canada; Department of Pediatrics, St. Michael's Hospital, Toronto, ON, Canada; Department of Pediatrics, Faculty of Medicine, University of Toronto, Toronto, ON, Canada. Electronic address: jonathon.maguire@utoronto.ca.
authors.forename: Jonathon L
authors.initials: JL
authors.lastname: Maguire
mesh_terms: D000328:Adult; D002585:Cesarean Section / Q000009:adverse effects / Q000706:statistics & numerical data*; D003430:Cross-Sectional Studies; D036861:Delivery, Obstetric / Q000706:statistics & numerical data*; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007751:Labor, Induced / Q000706:statistics & numerical data*; D008297:Male; D009864:Ontario / Q000453:epidemiology; D011159:Population Surveillance; D011247:Pregnancy; D047928:Premature Birth / Q000453:epidemiology*; D012044:Regression Analysis; D012307:Risk Factors
keywords: cesarean delivery; late preterm; maternal health; obstetric intervention; risk factors