title: Reoccurrence of retained placenta at vaginal delivery: an observational study.
abstract: OBJECTIVE
  To estimate the prevalence and validate the diagnosis of retained placenta in nulliparous women and the risk of reoccurrence at subsequent vaginal delivery.
  
  
  METHODS
  Nested cohort study.
  
  
  METHODS
  Department of Gynecology and Obstetrics, university-affiliated teaching hospital.
  
  
  METHODS
  10 334 nulliparous singleton pregnancies who delivered vaginally at the hospital during 2000-2009.
  
  
  METHODS
  Data from a computerized database information system were used to identify 287 women who had an ICD-10 diagnosis of retained placenta and 572 randomly selected controls matched by the date of first delivery. At chart review the diagnosis was confirmed by: (1) excessive bleeding <30 minutes after delivery without placental separation, (2) placenta not separated 30 minutes after delivery or (3) confirmation of retained placental tissue >2 hours postpartum.
  
  
  METHODS
  Confirmation of the diagnosis and prevalence of retained placenta. Risk of reoccurrence in a subsequent vaginal delivery.
  
  
  RESULTS
  The prevalence of retained placenta increased from 2.8 to 7.0% after confirmation according to the set criteria. Of the selected women, 48.4% had a subsequent vaginal delivery. Of these women, 25.3% (23/91) with a previous retained placenta and 5.3% (11/206) without previously retained placenta, experienced retained placenta in subsequent delivery. This corresponds to an adjusted odds ratio of 5.5 (95% confidence interval 2.6-12.7) in the multivariate analysis for recurrence of retained placenta in a subsequent vaginal delivery.
  
  
  CONCLUSIONS
  The use of the ICD-10 diagnosis of retained placenta underestimated the prevalence. The risk of reoccurrence of retained placenta is significantly increased in a subsequent vaginal delivery.
authors.affiliation: Department of Obstetrics & Gynecology, Hillerød Hospital, University of Copenhagen, Hillerød, Denmark. sysnikolajsen@gmail.com
authors.forename: Sys
authors.initials: S
authors.lastname: Nikolajsen
authors.forename: Ellen Christine Leth
authors.initials: EC
authors.lastname: Løkkegaard
authors.forename: Thomas
authors.initials: T
authors.lastname: Bergholt
mesh_terms: D000328:Adult; D036861:Delivery, Obstetric / Q000706:statistics & numerical data*; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006801:Humans; D007749:Labor Stage, Third; D018457:Placenta, Retained / Q000453:epidemiology*; D011181:Postnatal Care / Q000706:statistics & numerical data*; D011247:Pregnancy; D015995:Prevalence; D012008:Recurrence; D012189:Retrospective Studies; D012307:Risk Factors; D016387:Women's Health; D055815:Young Adult