Abstract

BACKGROUND Because there is no consensual method of assessing postpartum blood loss, the comparability and relevance of the postpartum hemorrhage-related literature is questionable. Quantitative blood loss assessment using a volumetric technique with a graduated collector bag has been proposed to overcome limitations of intervention-based outcomes but remains partly subjective and potentially biased by amniotic fluid or missed out-of-bag losses. Calculated blood loss based on laboratory parameters has been published and used as an objective method expected to reflect total blood loss, but few studies have compared quantitative with calculated blood loss. OBJECTIVE This study aimed to compare the distribution of postpartum blood loss after vaginal delivery assessed by two methods - quantitative and calculated blood loss - and the incidence of abnormal blood loss with each method. STUDY DESIGN The data came from the merged database of 3 multicenter, randomized controlled trials, all testing different interventions to prevent postpartum blood loss in individuals with a singleton live fetus ≥ 35 weeks, born vaginally. All 3 trials measured blood loss volume by using a graduated collector bag. Hematocrit was measured in the eighth or ninth month of gestation and on day 2 postpartum. The two primary outcomes were: quantitative blood loss defined by the total volume of blood loss measured in a graduated collector bag, and calculated blood loss mathematically defined from the peripartum hematocrit change (estimated blood volume × [(antepartum hematocrit - postpartum hematocrit)/antepartum hematocrit], where estimated blood volume (mL) = booking weight (kg) × 85). We modelled the association between positive quantitative blood loss and positive calculated blood loss with polynomial regression and calculated the Spearman correlation coefficient. RESULTS Among the 8341 individuals included in this analysis, the median quantitative blood loss (100 mL, interquartile range 50-275) was significantly lower than the median calculated blood loss (260 mL, interquartile range 0-630) (P<.05). The incidence of abnormal blood loss was lower with quantitative blood loss than calculated blood loss for blood loss ≥ 500 mL, ≥ 1000 mL and ≥ 2000 mL, respectively, it was 9.6% (799/8341) vs 32.3% (2691/8341), 2.1% (176/8341) vs 11.5% (959/8341), and 0.1% (10/8341) vs 1.4% (117/8341); (P<.05). Quantitative blood loss and calculated blood loss were significantly but moderately correlated (Spearman coefficient=0.44; P<.05). The association between them was not linear, and their difference tended to increase with blood loss. Negative calculated blood loss values occurred in 23% (1958/8341) of individuals; among them, more than 99% (1939/1958) had quantitative blood loss ≤ 500 mL. CONCLUSION Quantitative and calculated blood loss were significantly but moderately correlated after vaginal delivery. However, clinicians should be aware that quantitative blood loss is lower than calculated blood loss, with a difference that tended to rise as blood loss increased.

Abstract

BACKGROUND Trials of interventions for PPH prevention and treatment rely on different measurement methods for the quantification of blood loss and identification of PPH. This study's objective was to compare measures of blood loss obtained from two different measurement protocols frequently used in studies. METHODS Nine hundred women presenting for vaginal delivery were randomized to a direct method (a calibrated delivery drape) or an indirect method (a shallow bedpan placed below the buttocks and weighing the collected blood and blood-soaked gauze/pads). Blood loss was measured from immediately after delivery for at least one hour or until active bleeding stopped. RESULTS Significantly greater mean blood loss was recorded by the direct than by the indirect measurement technique (253.9 mL and 195.3 mL, respectively; difference = 58.6 mL (95% CI: 31-86); p < 0.001). Almost twice as many women in the direct than in the indirect group measured blood loss > 500 mL (8.7% vs. 4.7%, p = 0.02). CONCLUSIONS The study suggests a real and significant difference in blood loss measurement between these methods. Research using blood loss measurement as an endpoint needs to be interpreted taking measurement technique into consideration. TRIAL REGISTRATION This study has been registered at clinicaltrials.gov as NCT01885845.