Blood Loss as a Function of Body Surface Area: Redefining Parameters of Obstetric Blood Loss

OBJECTIVE: To identify average blood loss in vaginal and cesarean deliveries in a cohort of women based on body surface area and compare this with the standard definitions. METHODS: In this descriptive study, we analyzed data from 459 deliveries. We identified the median estimated blood loss across the sample. Using body surface area, we calculated the total blood volume for each woman and represented estimated blood loss as a percentage of total blood volume. For each quintile of body surface area, we determined the median estimated blood loss at delivery, the median total blood volume, and the volumes of blood loss that represent 5%, 10% and 15% of total blood volume, respectively. RESULTS: A total of 459 women met inclusion criteria. Median body surface area was 1.9 m 2 and median total blood volume was 5,046 mL. Median estimated blood loss was 300 mL and represented 5.9% of total blood volume. For each body surface area quintile, median estimated blood loss and percent total blood volume were: quintile 1, 250 mL, 5.7% total blood volume; quintile 2, 400 mL, 8.5% total blood volume; quintile 3, 300 mL, 5.9% total blood volume, quintile 4, 300 mL, 5.6% total blood volume, and quintile 5, 400 mL, 6.7% total blood volume. CONCLUSION: Redefining obstetric blood loss as a percentage of total blood volume rather than one universal value may help appropriate targeting of interventions.