Patients who gave birth vaginally, participating in the TRACOR, CYTOCINON, and TRAAP randomised controlled trials (RCTs) in several French maternity units (n= 8,341).
This study aimed to compare the distribution of postpartum blood assessed by two methods - quantitative and calculated blood loss - and the incidence of abnormal blood loss with each method.
The data came from 3 RCTs testing different interventions to prevent postpartum blood loss. All 3 trials measured blood loss volume by using a graduated collector bag. The authors modelled the association between positive quantitative blood loss and positive calculated blood loss with polynomial regression and calculated the Spearman correlation coefficient. The median quantitative blood loss (100 mL, IQR= 50, 275) was significantly lower than the median calculated blood loss (260 mL, IQR= 0, 630). The incidence of abnormal blood loss was lower with quantitative blood loss than calculated blood loss. Quantitative blood loss and calculated blood loss were significantly but moderately correlated (Spearman coefficient= 0.44). The association between them was not linear, and their difference tended to increase with blood loss. Negative calculated blood loss values occurred in 23% (1,958/8,341) of individuals; among them, more than 99% (1,939/1,958) had quantitative blood loss ≤ 500 mL.