INTRODUCTION
The goal of defining a blood loss threshold that defines a significant obstetrical hemorrhage (OBH) is to find a sensitive and specific quantity of obstetrical bleeding that should trigger closer monitoring or interventions to prevent perinatal morbidity and mortality.1 Historical definitions of obstetric hemorrhage have primarily been based in expert-opinion rather than evidence-based thresholds of morbidity or mortality.2
The first proposed definition of postpartum hemorrhage traces back to a report published after an informal meeting of experts in 1989 at the World Health Organization, which defined PPH as “greater than 500mL blood loss from the genital tract after the delivery of a baby” but also acknowledged this as an “arbitrary figure” and “not always of great clinical significance.”2,3 In 2014, as part of the “reVITALize” initiative, the American College of Obstetricians and Gynecologists (ACOG) established a new definition of OBH as 1,000cc of cumulative blood loss regardless of route of delivery or specific vital sign changes associated with blood loss.4 This initiative focused on decreasing morbidity and mortality by standardizing the obstetrical definitions and approaches utilized by providers in the United States in the care of birthing people in labor. However, while a small cohort of historical data from Pritchard et al., which followed peripartum patients using 51 chromium labeled red cells, demonstrated mean losses to be around 500mL in vaginal deliveries and around 1000mL in cesarean deliveries, there is little contemporary data that demonstrates a specific association between obstetric blood loss of 1,000cc and clinically significant adverse perinatal outcomes.5
To address this “arbitrary” definition of OBH, we investigate the cumulative quantitative blood loss (QBL) associated with increased risk of severe obstetric hemorrhage-related morbidity (OBH-M). We also seek to compare the predictiveness for OBH-M of the current definition of OBH to an alternate definition derived from our cohort.