title: Duration of labor and the risk of severe postpartum hemorrhage: A case-control study.
abstract: OBJECTIVE
  Our main objective was to investigate the association between duration of active labor and severe postpartum hemorrhage. We examined the effect of the total duration of active labor, the effect of each stage of active labor, and the gradient effect of duration of labor on severe postpartum hemorrhage.
  
  
  METHODS
  A case-control study was generated from a source population of all women admitted for delivery at Oslo University Hospital and Drammen Hospital in Buskerud municipality during the time period January 1, 2008 to December 31, 2011. The study population included all cases of severe postpartum hemorrhage (n = 859) and a random sample of controls (n = 1755). Severe postpartum hemorrhage was defined as postpartum blood loss ≥1500 mL or need for blood transfusion. Prolonged labor was defined as duration of active labor >12 hours according to the definition of the World Health Organization. We used logistic multivariable regression in the analysis.
  
  
  RESULTS
  We observed a significantly longer mean duration of labor in women who experienced severe postpartum hemorrhage compared to controls (5.4 versus 3.8 hours, p<0.001). Women with severe postpartum hemorrhage also had a longer duration of all stages of active labor compared to controls. The association between the duration of active labor and severe postpartum changed from a linear dose-response association to a threshold association after adjusting for augmentation with oxytocin, induction of labor, primiparity, and fever during labor. Compared to controls, women with severe postpartum hemorrhage were more likely to have a prolonged labor >12 hours (adjusted odds ratio = 2.44, 95% confidence interval: 1.69-3.53, p< 0.001).
  
  
  CONCLUSIONS
  Prolonged active labor (duration >12 hours) was associated with severe postpartum hemorrhage. Increased vigilance seems required when the labor is prolonged to reduce the risk of severe postpartum hemorrhage.
authors.affiliation: Division of Gynecology and Obstetrics, Oslo University Hospital, Oslo, Norway.|Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway.
authors.forename: Lill Trine
authors.identifier: http://orcid.org/0000-0001-8979-1563
authors.initials: LT
authors.lastname: Nyfløt
authors.affiliation: Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway.
authors.forename: Babill
authors.initials: B
authors.lastname: Stray-Pedersen
authors.affiliation: Norwegian Institute of Public Health, Oslo, Norway.|Norwegian National Advisory Unit on Women's Health, Oslo University Hospital, Oslo, Norway.
authors.forename: Lisa
authors.initials: L
authors.lastname: Forsén
authors.affiliation: Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway.|Norwegian National Advisory Unit on Women's Health, Oslo University Hospital, Oslo, Norway.
authors.forename: Siri
authors.initials: S
authors.lastname: Vangen
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007743:Labor, Obstetric; D006473:Postpartum Hemorrhage / Q000453:epidemiology*; D011247:Pregnancy; D012307:Risk Factors; D013548:Sweden; D055815:Young Adult