title: Second-trimester placental location and postpartum hemorrhage.
abstract: OBJECTIVE
  The purpose of this study was to assess whether low placentation in the second trimester is an independent risk factor for postpartum hemorrhage.
  
  
  METHODS
  A retrospective cohort study of women undergoing transvaginal sonography between 18 weeks' and 23 weeks 6 days' gestation was conducted. Patients were subdivided into three groups: low-lying placenta (0.1-2.5 cm), marginal previa (touching but not overlapping the os), and complete previa (covering the os). Low placentation was used as a descriptive for all cases (low-lying placenta, marginal previa, and complete previa) in this study. A group of randomly identified control patients with normal placentation was selected for comparison.
  
  
  RESULTS
  During the period of study, 410 women with low placentation were identified. Compared to controls, patients with second-trimester low placentation had increased rates of postpartum hemorrhage and uterotonic use. These increased risks persisted even among women in whom the low placentation resolved (odds ratio, 2.72; 95% confidence interval, 1.46-5.07; odds ratio, 2.18; 95% confidence interval, 1.24-3.84).
  
  
  CONCLUSIONS
  Women with a second-trimester diagnosis of low placentation are at increased risk of postpartum hemorrhage.
authors.affiliation: Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, Northwestern University, Feinberg School of Medicine, Chicago, IL, USA. s.osmundson@gmail.com
authors.forename: Sarah S
authors.initials: SS
authors.lastname: Osmundson
authors.forename: Amy E
authors.initials: AE
authors.lastname: Wong
authors.forename: Susan E
authors.initials: SE
authors.lastname: Gerber
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D016015:Logistic Models; D010923:Placenta Previa / Q000453:epidemiology; D010929:Placentation / Q000502:physiology*; D006473:Postpartum Hemorrhage / Q000453:epidemiology* / Q000503:physiopathology*; D011247:Pregnancy; D011256:Pregnancy Outcome; D011262:Pregnancy Trimester, Second / Q000502:physiology*; D012307:Risk Factors