title: Previous prelabor or intrapartum cesarean delivery and risk of placenta previa.
abstract: OBJECTIVE
  The purpose of this study was to examine the association between previous cesarean delivery and subsequent placenta previa while distinguishing cesarean delivery before the onset of labor from intrapartum cesarean delivery.
  
  
  METHODS
  We conducted a retrospective cohort study of electronic medical records from 20 Utah hospitals (2002-2010) with restriction to the first 2 singleton deliveries of nulliparous women at study entry (n=26,987). First pregnancy delivery mode was classified as (1) vaginal (reference), (2) cesarean delivery before labor onset (prelabor), or (3) cesarean delivery after labor onset (intrapartum). Risk of second delivery previa was estimated by previous delivery mode with the use of logistic regression and was adjusted for maternal age, insurance, smoking, comorbidities, previous pregnancy loss, and history of previa.
  
  
  RESULTS
  Most first deliveries were vaginal (82%; n=22,142), followed by intrapartum cesarean delivery (14.6%; n=3931), or prelabor cesarean delivery (3.4%; n=914). Incidence of second delivery previa was 0.29% (n=78) and differed by previous delivery mode: vaginal, 0.24%; prelabor cesarean delivery, 0.98%; intrapartum cesarean delivery, 0.38% (P<.001). Relative to vaginal delivery, previous prelabor cesarean delivery was associated with an increased risk of second delivery previa (adjusted odds ratio, 2.62; 95% confidence interval, 1.24-5.56). There was no significant association between previous intrapartum cesarean delivery and previa (adjusted odds ratio, 1.22; 95% confidence interval, 0.68-2.19).
  
  
  CONCLUSIONS
  Previous prelabor cesarean delivery was associated with a >2-fold significantly increased risk of previa in the second delivery, although the approximately 20% increased risk of previa that was associated with previous intrapartum cesarean delivery was not significant. Although rare, the increased risk of placenta previa after previous prelabor cesarean delivery may be important when considering nonmedically indicated prelabor cesarean delivery.
authors.affiliation: Epidemiology Branch, Division of Intramural Population Health Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD; Department of Family Science, University of Maryland School of Public Health, College Park, MD.
authors.forename: Katheryne L
authors.initials: KL
authors.lastname: Downes
authors.affiliation: Epidemiology Branch, Division of Intramural Population Health Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD.
authors.forename: Stefanie N
authors.initials: SN
authors.lastname: Hinkle
authors.affiliation: Epidemiology Branch, Division of Intramural Population Health Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD.
authors.forename: Lindsey A
authors.initials: LA
authors.lastname: Sjaarda
authors.affiliation: Biostatistics and Bioinformatics Branch, Division of Intramural Population Health Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD.
authors.forename: Paul S
authors.initials: PS
authors.lastname: Albert
authors.affiliation: Epidemiology Branch, Division of Intramural Population Health Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD. Electronic address: Katherine.grantz@nih.gov.
authors.forename: Katherine L
authors.initials: KL
authors.lastname: Grantz
mesh_terms: D000293:Adolescent; D000328:Adult; D002585:Cesarean Section / Q000706:statistics & numerical data*; D015331:Cohort Studies; D036861:Delivery, Obstetric / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D016015:Logistic Models; D008423:Maternal Age; D008875:Middle Aged; D016017:Odds Ratio; D010923:Placenta Previa / Q000453:epidemiology*; D011247:Pregnancy; D012189:Retrospective Studies; D012307:Risk Factors; D014589:Utah / Q000453:epidemiology; D055815:Young Adult
keywords: cesarean delivery; intrapartum; placenta previa; prelabor