Estimation of blood loss after cesarean section and vaginal delivery has low validity with a tendency to exaggeration

Background. Excessive bleeding is one of the major threats to women at childbirth. The aim of this study was to validate estimation of blood loss during delivery. Methods. Bleeding was estimated after 29 elective cesarean sections and 26 vaginal deliveries and compared to blood loss measured by extraction of hemoglobin using the alkaline hematin method, according to Newton. Results. Inter‐individual agreement of estimation showed good results. Estimated loss in comparison with measured loss resulted in an over‐estimation. In vaginally delivered women, there was no correlation between estimated and measured blood loss (r² = 0.13), and in women delivered by elective cesarean section, the correlation was moderate (r² = 0.55). Agreement, according to Bland and Altman, indicated that measured blood loss could vary from 570 ml less to 342 ml more than estimated blood loss. Conclusions. The standard procedure of estimation of obstetric bleeding was found to be unreliable. In this study, blood loss was over‐estimated in cesareans. In vaginal deliveries, there seemed to be no correlation. Estimated blood loss as a quality indicator or as a variable in studies comparing complications must be used with caution. For clinical purposes, estimation of blood loss and measurement of post partum hemoglobin is of low value and may lead to the wrong conclusions.