title: Accuracy of Estimated Blood Loss in Predicting Need for Transfusion after Delivery.
abstract: OBJECTIVE
  The definition of postpartum hemorrhage (PPH) was developed more than 50 years ago. Since then, the obstetric population has changed dramatically. We sought to determine how well we estimated blood loss (EBL) and find thresholds predicting need for transfusion.
  
  
  METHODS
  We performed a prospective cohort study from 2010 to 2012, comparing those who needed transfusion postpartum and those who did not. EBL, calculated EBL (cEBL), and change in hematocrit were calculated for patients who did not receive transfusion, and EBL was calculated for those who did receive transfusion, stratified by delivery type. Receiver operator curves were created and optimal thresholds of EBL to predict transfusion were estimated.
  
  
  RESULTS
  Among 4,804 patients, transfusion was required for 0.65% of vaginal and 8.7% of cesarean deliveries. Median EBL was higher in women requiring transfusion. A weak correlation was noted between EBL and cEBL for all deliveries. Thresholds of 500 mL blood loss for vaginal delivery and 1,000 mL for cesarean had the best predictive ability for transfusion.
  
  
  CONCLUSIONS
  In this modern obstetric, cohort EBL is weakly correlated with cEBL, suggesting that accuracy of clinical estimates of blood loss is modest. However, EBL predicts need for transfusion, with optimal thresholds of 500 mL for a vaginal delivery and 1,000 mL in a cesarean. This validates the traditional definitions of PPH in our modern population.
authors.affiliation: Department of Obstetrics and Gynecology, Washington University School of Medicine, St. Louis, Missouri.
authors.forename: Shayna N
authors.initials: SN
authors.lastname: Conner
authors.affiliation: Department of Obstetrics and Gynecology, Washington University School of Medicine, St. Louis, Missouri.
authors.forename: Methodius G
authors.initials: MG
authors.lastname: Tuuli
authors.affiliation: Department of Obstetrics and Gynecology, Washington University School of Medicine, St. Louis, Missouri.
authors.forename: Ryan
authors.initials: R
authors.lastname: Colvin
authors.affiliation: Department of Obstetrics and Gynecology, Washington University School of Medicine, St. Louis, Missouri.
authors.forename: Anthony L
authors.initials: AL
authors.lastname: Shanks
authors.affiliation: Department of Obstetrics and Gynecology, Washington University School of Medicine, St. Louis, Missouri.
authors.forename: George A
authors.initials: GA
authors.lastname: Macones
authors.affiliation: Department of Obstetrics and Gynecology, Washington University School of Medicine, St. Louis, Missouri.
authors.forename: Alison G
authors.initials: AG
authors.lastname: Cahill
mesh_terms: D000328:Adult; D001803:Blood Transfusion; D002585:Cesarean Section; D015331:Cohort Studies; D036861:Delivery, Obstetric; D005260:Female; D006400:Hematocrit; D006801:Humans; D006473:Postpartum Hemorrhage / Q000175:diagnosis* / Q000628:therapy; D011247:Pregnancy; D011446:Prospective Studies; D012372:ROC Curve; D055815:Young Adult