title: Risk Factors for Severe Postpartum Hemorrhage After Cesarean Delivery: Case-Control Studies.
abstract: Women who undergo intrapartum caesarean delivery (CD) are at increased risk of postpartum hemorrhage (PPH) compared with those undergoing prelabor CD. To determine whether the presence and strength of the associations between individual risk factors and severe PPH vary among women undergoing prelabor CD or intrapartum CD, stratified analyses are needed according to CD subtype.
  
  
  
  To identify risk factors for severe PPH within 2 distinct CD populations, prelabor CD and intrapartum CD, we performed 2 case-control studies. Women in each study cohort delivered at a tertiary obstetric center in the United States between 2002 and 2012. For each study, cases were women who had a blood loss ≥1500 mL or who received an intraoperative or postoperative transfusion up to 48 hours after delivery. Risk factors for severe PPH among women undergoing prelabor CD or intrapartum CD were examined in separate logistic regression models.
  
  
  
  For prelabor CD, we identified 269 cases and 550 controls. Clinical factors with the highest adjusted odds for severe PPH during prelabor CD were general anesthesia (adjusted odds ratio [aOR] = 22.3; 95% confidence interval [CI], 4.9-99.9; reference group = spinal anesthesia), multiple pregnancies (aOR = 8.0; 95% CI, 4.2-15.0; reference group = singleton pregnancy), and placenta previa (aOR = 6.3; 95% CI, 3.4-11.8). For intrapartum CD, we identified 278 cases and 572 controls. Clinical factors with the highest adjusted odds for severe PPH during intrapartum CD were general anesthesia (aOR = 5.4; 95% CI, 1.7-17.1), multiple pregnancies (aOR = 3.2; 95% CI, 1.7-6.3), and a predelivery hemoglobin ≤ 9.9 g/dL (aOR = 3.0; 95% CI, 1.3-6.9; reference group = predelivery hemoglobin ≥ 11 g/dL).
  
  
  
  Women who undergo prelabor CD and intrapartum CD have several shared risk factors for severe PPH (general anesthesia and multiple pregnancies). However, the risk factor profiles for severe PPH differed between these CD cohorts. Recognizing these differences may be important when planning resources and interventions for high-risk patients undergoing either prelabor or intrapartum CD.
authors.affiliation: From the Departments of *Anesthesiology, Perioperative, and Pain Medicine; †Obstetrics and Gynecology; and ‡Health Research and Policy (Division of Epidemiology), Stanford University School of Medicine, Stanford, California.
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Butwick
authors.forename: Bharathi
authors.initials: B
authors.lastname: Ramachandran
authors.forename: Priya
authors.initials: P
authors.lastname: Hegde
authors.forename: Edward T
authors.initials: ET
authors.lastname: Riley
authors.forename: Yasser Y
authors.initials: YY
authors.lastname: El-Sayed
authors.forename: Lorene M
authors.initials: LM
authors.lastname: Nelson
mesh_terms: D000328:Adult; D000768:Anesthesia, General / Q000009:adverse effects; D016022:Case-Control Studies; D002585:Cesarean Section / Q000009:adverse effects*; D015331:Cohort Studies; D036861:Delivery, Obstetric / Q000009:adverse effects; D005260:Female; D006801:Humans; D007432:Intraoperative Period; D007743:Labor, Obstetric; D009774:Obstetrics; D036801:Parturition; D011184:Postoperative Period; D006473:Postpartum Hemorrhage / Q000175:diagnosis*; D049590:Postpartum Period; D011247:Pregnancy; D011336:Probability; D012044:Regression Analysis; D012307:Risk Factors; D065227:Transfusion Reaction