title: Prior cesarean and the risk for placenta previa on second-trimester ultrasonography.
abstract: OBJECTIVE
  To determine whether the increased risk of placenta previa at delivery in patients with a prior cesarean results from an increased risk of abnormal implantation or a lower likelihood of resolution.
  
  
  METHODS
  A hospital-based, case-control study was performed. Cases were defined as singleton pregnancies with a placenta previa on second-trimester ultrasonography. Controls, chosen randomly from patients without a placenta previa on second-trimester ultrasonography, were matched 3:1 with cases. Odds ratios (OR) were calculated, controlling for other independent risk factors for previa: age, parity, race, and smoking.
  
  
  RESULTS
  There were 88 cases identified and 264 controls. Twenty cases (22.7%) and 35 controls (13.3%) had a history of prior cesarean delivery. Previous cesarean delivery was an independent risk factor for previa on second-trimester ultrasonography (OR 1.92, 95% confidence interval [CI] 1.04-3.55), as was the number of cesareans (OR 1.62, 95% CI 1.12-2.34). However, neither retained their significance after adjusting for other known risk factors for previa (OR 1.50, 95% CI 0.77-2.92, and OR 1.40, 95% CI 0.93-2.10, respectively). At delivery, a history of cesarean was associated with a 3-fold increased risk of previa.
  
  
  CONCLUSIONS
  A previous cesarean delivery did not increase the odds for detecting a placenta previa on second-trimester ultrasonography. At delivery, a previous cesarean was associated with a previa, suggesting a lower likelihood of resolution.
authors.affiliation: Department of Obstetrics and Gynecology, University of North Carolina School of Medicine, Chapel Hill, North Carolina, USA.
authors.forename: S Katherine
authors.initials: SK
authors.lastname: Laughon
authors.forename: Honor M
authors.initials: HM
authors.lastname: Wolfe
authors.forename: Anthony G
authors.initials: AG
authors.lastname: Visco
mesh_terms: D000328:Adult; D000367:Age Factors; D016022:Case-Control Studies; D002585:Cesarean Section / Q000009:adverse effects*; D016001:Confidence Intervals; D005260:Female; D006801:Humans; D015994:Incidence; D016017:Odds Ratio; D010298:Parity; D010923:Placenta Previa / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000209:etiology*; D011247:Pregnancy; D011256:Pregnancy Outcome; D011262:Pregnancy Trimester, Second; D011336:Probability; D011379:Prognosis; D012016:Reference Values; D018570:Risk Assessment; D016216:Ultrasonography, Prenatal