title: Previous cesarean section and abortion as risk factors for developing placenta previa.
abstract: OBJECTIVE
  To determine the risk of subsequent occurrence of placenta previa in women with a history of previous cesarean sections and/or spontaneous and induced abortions.
  
  
  METHODS
  A retrospective analysis of all single gestation deliveries at National University Hospital of Singapore from 1993-1997 was done. Women with placenta previa were identified by clinical or ultrasonographic diagnosis.
  
  
  RESULTS
  Of the 16,169 singleton deliveries, 164 women (1.0%) had placenta previa. Women with placenta previa had a significantly higher incidence of previous cesarean sections (p < 0.001). Among the 164 women with placenta previa, women with 1, 2, and 3 previous cesarean sections had 2.2 (95% CI 1.4, 3.4), 4.1 (95% CI 1.9, 8.8) and 22.4 (95% CI 6.4, 78.3) times increased risk of developing placenta previa respectively. Similarly, women with 2 or more previous abortions had a 2.1 (95% CI 1.2, 3.5) times increased risk of subsequently developing placenta previa.
  
  
  CONCLUSIONS
  There is a strong association between previous cesarean section and risk of subsequent development of placenta previa. This risk increased with the number of previous cesarean sections. Increasing frequency of abortions was also found to predispose a woman to placenta previa.
authors.affiliation: Department of Obstetrics and Gynaecology, National University Hospital, Singapore.
authors.forename: M S
authors.initials: MS
authors.lastname: Hendricks
authors.forename: Y H
authors.initials: YH
authors.lastname: Chow
authors.forename: B
authors.initials: B
authors.lastname: Bhagavath
authors.forename: K
authors.initials: K
authors.lastname: Singh
mesh_terms: D000028:Abortion, Induced / Q000009:adverse effects*; D000022:Abortion, Spontaneous / Q000150:complications*; D000328:Adult; D002585:Cesarean Section / Q000009:adverse effects*; D005260:Female; D006801:Humans; D010923:Placenta Previa / Q000209:etiology*; D011247:Pregnancy; D012189:Retrospective Studies; D012307:Risk Factors