title: Risk factors for severe postpartum hemorrhage: a case-control study.
abstract: In high-income countries, the incidence of severe postpartum hemorrhage (PPH) has increased. This has important public health relevance because severe PPH is a leading cause of major maternal morbidity. However, few studies have identified risk factors for severe PPH within a contemporary obstetric cohort.
  
  
  
  We performed a case-control study to identify risk factors for severe PPH among a cohort of women who delivered at one of three hospitals in Norway between 2008 and 2011. A case (severe PPH) was classified by an estimated blood loss ≥1500 mL or the need for blood transfusion for excessive postpartum bleeding. Using logistic regression, we applied a pragmatic strategy to identify independent risk factors for severe PPH.
  
  
  
  Among a total of 43,105 deliveries occurring between 2008 and 2011, we identified 1064 cases and 2059 random controls. The frequency of severe PPH was 2.5% (95% confidence interval (CI): 2.32-2.62). The most common etiologies for severe PPH were uterine atony (60%) and placental complications (36%). The strongest risk factors were a history of severe PPH (adjusted OR (aOR) = 8.97, 95% CI: 5.25-15.33), anticoagulant medication (aOR = 4.79, 95% CI: 2.72-8.41), anemia at booking (aOR = 4.27, 95% CI: 2.79-6.54), severe pre-eclampsia or HELLP syndrome (aOR = 3.03, 95% CI: 1.74-5.27), uterine fibromas (aOR = 2.71, 95% CI: 1.69-4.35), multiple pregnancy (aOR = 2.11, 95% CI: 1.39-3.22) and assisted reproductive technologies (aOR = 1.88, 95% CI: 1.33-2.65).
  
  
  
  Based on our findings, women with a history of severe PPH are at highest risk of severe PPH. As well as other established clinical risk factors for PPH, a history of severe PPH should be included as a risk factor in the development and validation of prediction models for PPH.
authors.affiliation: Division of Gynecology and Obstetrics, Oslo University Hospital, Rikshospitalet, P.O.box 4950, Nydalen, 0424, Oslo, Norway. l.t.nyflot@medisin.uio.no.|Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, P.O. box 1171, Blindern, 0318, Oslo, Norway. l.t.nyflot@medisin.uio.no.|Department of Gynecology and Obstetrics, Drammen Hospital, P.O.box 800, 3004, Drammen, Norway. l.t.nyflot@medisin.uio.no.
authors.forename: Lill Trine
authors.initials: LT
authors.lastname: Nyfløt
authors.affiliation: Oslo Centre of Biostatistics and Epidemiology, Research Support Services, Sogn Arena, P.O.box 4950, Nydalen, 0424, Oslo, Norway.
authors.forename: Irene
authors.initials: I
authors.lastname: Sandven
authors.affiliation: Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, P.O. box 1171, Blindern, 0318, Oslo, Norway.
authors.forename: Babill
authors.initials: B
authors.lastname: Stray-Pedersen
authors.affiliation: Division of Gynecology and Obstetrics, Oslo University Hospital, Rikshospitalet, P.O.box 4950, Nydalen, 0424, Oslo, Norway.
authors.forename: Silje
authors.initials: S
authors.lastname: Pettersen
authors.affiliation: Division of Gynecology and Obstetrics, Oslo University Hospital, Rikshospitalet, P.O.box 4950, Nydalen, 0424, Oslo, Norway.
authors.forename: Iqbal
authors.initials: I
authors.lastname: Al-Zirqi
authors.affiliation: Department of Gynecology and Obstetrics, Drammen Hospital, P.O.box 800, 3004, Drammen, Norway.
authors.forename: Margit
authors.initials: M
authors.lastname: Rosenberg
authors.affiliation: Division of Gynecology and Obstetrics, Oslo University Hospital, Rikshospitalet, P.O.box 4950, Nydalen, 0424, Oslo, Norway.|Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, P.O. box 1171, Blindern, 0318, Oslo, Norway.
authors.forename: Anne Flem
authors.initials: AF
authors.lastname: Jacobsen
authors.affiliation: Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, P.O. box 1171, Blindern, 0318, Oslo, Norway.|Norwegian National Advisory Unit on Women's Health, Oslo University Hospital, P.o.box 4950, Nydalen, 0424, Oslo, Norway.
authors.forename: Siri
authors.initials: S
authors.lastname: Vangen
mesh_terms: D000328:Adult; D000740:Anemia / Q000150:complications; D000925:Anticoagulants / Q000009:adverse effects; D001803:Blood Transfusion / Q000706:statistics & numerical data; D016022:Case-Control Studies; D015331:Cohort Studies; D036861:Delivery, Obstetric / Q000009:adverse effects*; D005260:Female; D006801:Humans; D007889:Leiomyoma / Q000150:complications; D016015:Logistic Models; D009664:Norway; D010922:Placenta Diseases / Q000209:etiology*; D006473:Postpartum Hemorrhage / Q000209:etiology*; D011225:Pre-Eclampsia / Q000209:etiology; D011247:Pregnancy; D011272:Pregnancy, Multiple; D027724:Reproductive Techniques, Assisted / Q000009:adverse effects; D012307:Risk Factors; D014593:Uterine Inertia / Q000209:etiology*; D014594:Uterine Neoplasms / Q000150:complications
chemical_list: D000925:Anticoagulants
keywords: Case-control study; High-risk; Obstetric interventions; Postpartum hemorrhage; Prediction; Predictors; Prevention; Risk factors