title: Incidence of and risk indicators for vasa praevia: a systematic review.
abstract: BACKGROUND
  Vasa praevia (VP) is a rare phenomenon that is assumed to increase the risk of severe complications, including fetal death. Critical data on its incidence are lacking, so there is no rational basis for prenatal screening.
  
  
  OBJECTIVE
  To review the literature on the incidence and risk indicators for VP.
  
  
  METHODS
  We searched OVID MEDLINE, OVID EMBASE, the Cochrane Library and PubMed for case-control and cohort studies on incidence and risk indicators for VP.
  
  
  METHODS
  Two reviewers selected studies and scored their methodological quality.
  
  
  METHODS
  We calculated the mean incidence of VP. We constructed 2 × 2 tables cross-classifying potential risk indicators against the incidence of VP to calculate common odds ratios and 95% confidence intervals, using the Mantel-Haenszel method.
  
  
  RESULTS
  We included 13 studies (two prospective cohort studies, ten retrospective cohort studies and one case-control study) reporting on 569 410 patients with 325 cases of VP. Based on ten included cohort studies providing information on the incidence, the mean incidence of VP was 0.60 per 1000 pregnancies. We identified five different risk indicators and markers for VP: second-trimester placenta praevia, conception by assisted reproductive technologies, a bilobed or succenturiate placenta, umbilical cord insertion in the lower third part of the uterus at first-trimester ultrasound and velamentous cord insertion. Almost 83% of the cases of VP had one or more risk indicators.
  
  
  CONCLUSIONS
  In view of the low incidence, screening for VP in an unselected population is not advised. Targeted screening of women with one or more risk indicators as a part of routine mid-gestation scanning should be considered.
  
  
  CONCLUSIONS
  Vasa praevia is more common in placenta praevia, conception by ART, velamentous cord insertion and bilobed placenta.
authors.affiliation: Department of Obstetrics and Gynaecology, Academic Medical Centre Amsterdam, Amsterdam, the Netherlands.
authors.forename: L
authors.initials: L
authors.lastname: Ruiter
authors.affiliation: Department of Obstetrics and Gynaecology, Vrije Universiteit Medical Centre, Amsterdam, the Netherlands.
authors.forename: N
authors.initials: N
authors.lastname: Kok
authors.affiliation: Medical Library, Academic Medical Centre, Amsterdam, the Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: Limpens
authors.affiliation: Department of Obstetrics and Gynaecology, University Medical Centre, Utrecht, the Netherlands.
authors.forename: J B
authors.initials: JB
authors.lastname: Derks
authors.affiliation: Department of Obstetrics and Gynaecology, Academic Medical Centre Amsterdam, Amsterdam, the Netherlands.
authors.forename: I M
authors.initials: IM
authors.lastname: de Graaf
authors.affiliation: The Robinson Institute, School of Paediatrics and Reproductive Health, University of Adelaide, Adelaide, SA, Australia.
authors.forename: Bwj
authors.initials: B
authors.lastname: Mol
authors.affiliation: Department of Obstetrics and Gynaecology, Academic Medical Centre Amsterdam, Amsterdam, the Netherlands.
authors.forename: E
authors.initials: E
authors.lastname: Pajkrt
mesh_terms: D005260:Female; D006801:Humans; D016017:Odds Ratio; D010920:Placenta / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D010923:Placenta Previa / Q000000981:diagnostic imaging / Q000453:epidemiology*; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011262:Pregnancy Trimester, Second; D027724:Reproductive Techniques, Assisted / Q000706:statistics & numerical data*; D012306:Risk; D018570:Risk Assessment; D016216:Ultrasonography, Prenatal; D014470:Umbilical Cord / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D055949:Vasa Previa / Q000453:epidemiology*
keywords: Incidence; risk factor; vasa praevia