title: Risks of adverse outcomes in the next birth after a first cesarean delivery.
abstract: OBJECTIVE
  To estimate the risks of cesarean first birth, compared with vaginal first birth, for adverse obstetric and perinatal outcomes in the second birth.
  
  
  METHODS
  Population-based retrospective cohort study of all singleton, second births in the South Australian perinatal data collection 1998 to 2003 comparing outcomes for 8,725 women who underwent a cesarean delivery for their first birth with 27,313 women who underwent a vaginal first birth. Predictor variables include age, indigenous status, smoking, pregnancy interval, medical and obstetric complications, gestation, patient type, hospital category, and history of ectopic pregnancy, miscarriage, stillbirth or termination of pregnancy.
  
  
  RESULTS
  The cesarean delivery cohort had increased risks for malpresentation (odds ratio [OR] 1.84, 95% confidence interval [CI] 1.65-2.06), placenta previa (OR 1.66, 95% CI 1.30-2.11), antepartum hemorrhage (OR 1.23, 95% CI 1.08-1.41), placenta accreta (OR 18.79, 95% CI 2.28-864.6), prolonged labor (OR 5.89, 95% CI 3.91-8.89), emergency cesarean (relative risk 9.37, 95% CI 8.98-9.76) and uterine rupture (OR 84.42, 95% CI 14.64-infinity), preterm birth (OR 1.17, 95% CI 1.04-1.31), low birth weight (OR 1.30, 95% CI 1.14-1.48), small for gestational age (OR 1.12, 95% CI 1.02-1.23), stillbirth (OR 1.56, 95% CI 1.04-2.32), and unexplained stillbirth (OR 2.34, 95% CI 1.26-4.37). The range of the number of primary cesarean deliveries needed to harm included 134 for one additional preterm birth, up to 1,536 for one additional placenta accreta.
  
  
  CONCLUSIONS
  Cesarean delivery is associated with increased risks for adverse obstetric and perinatal outcomes in the subsequent birth. However, some risks may be due to confounding factors related to the indication for the first cesarean.
  
  
  METHODS
  II.
authors.affiliation: Pregnancy Outcome Unit and Health Statistics Unit, Epidemiology Branch, Department of Health, Rundle Mall, Adelaide, SA 5000, Australia. robyn.kennare@health.sa.gov.au
authors.forename: Robyn
authors.initials: R
authors.lastname: Kennare
authors.forename: Graeme
authors.initials: G
authors.lastname: Tucker
authors.forename: Adrian
authors.initials: A
authors.lastname: Heard
authors.forename: Annabelle
authors.initials: A
authors.lastname: Chan
mesh_terms: D000328:Adult; D002585:Cesarean Section; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D007744:Obstetric Labor Complications / Q000453:epidemiology*; D011247:Pregnancy; D012189:Retrospective Studies; D018570:Risk Assessment; D013021:South Australia / Q000453:epidemiology; D050497:Stillbirth / Q000453:epidemiology*