Study questions value of quantitative blood loss measurement in caesarean births

Quantitative blood loss (QBL) is only marginally better than estimated blood loss (EBL) in measuring blood loss and detecting postpartum haemorrhage during caesarean deliveries, according to a new study presented at the 2022 Annual Clinical & Scientific Meeting of the American College of Obstetricians and Gynecologists (ACOG 2022).

“Traditionally, during deliveries, blood loss was estimated visually. More recently, QBL has been implemented to increase blood loss assessment accuracy,” the researchers said, noting that “given the time and resources necessary to calculate QBL, this study questions its utilization and/or superiority to EBL in the detection of postpartum haemorrhage.”

Data from 486 women who gave caesarean births between 1 December 2018 and 1 December 2019 were retrospectively reviewed; all participants had available EBL and QBL measurements. As the gold-standard reference, calculated blood loss (CBL) was gauged using maternal height and weight, as well as pre- and postdelivery haematocrit. Haemorrhage, a study outcome, was defined as blood loss ≥1,000 mL.

CBL measured a median blood loss of 896.2 mL during birth. In comparison, both EBL and QBL resulted in significantly lower measurements, with respective median values of 600.0 and 547.5 mL. [ACOG 2022, abstract A144]

In terms of detecting postpartum haemorrhage, EBL showed high specificity relative to CBL (89.7 percent), but very low sensitivity (12.0 percent). The same was true for QBL, though this had marginally better specificity (94.4 percent) and sensitivity (22.6 percent) than EBL.

Meanwhile, EBL showed a better positive predictive value for haemorrhage than QBL, both relative to CBL (89.7 percent vs 76.6 percent). The negative predictive values of both EBL and QBL were poor (58.2 percent and 60.2 percent, respectively).

Overall, QBL was able to detect only six more cases of postpartum haemorrhages than EBL (35 vs 29). CBL, on the other hand, identified 153 such episodes.

The present findings added to a growing debate regarding the accuracy and clinical utility of QBL in measuring blood loss during caesarean deliveries. In contrast to the current results, a 2021 retrospective observational study found that, though the rates of transfusion did not ultimately differ, QBL trumped EBL in predicting a ≥10-point drop in haematocrit or the need for blood transfusion. [Cureus 2021;13:e13591]

Similarly, a 2020 study compared visual blood loss estimation with colorimetric quantification and deemed that QBL led to more accurate activations of postpartum haemorrhage clinical protocols, “[reducing] the number of identified postpartum haemorrhages by more than 50 percent over visual EBL and may have reduced the resources used as part of care.” [J Obstet Gynecol Neonatal Nurs 2020;49:137–143]

Meanwhile, several studies also concur with the present findings. In 2019, a report revealed that while implementing a QBL protocol led to a significantly higher rate of postpartum haemorrhage detection, it did not substantially outperform EBL in predicting patients’ need for transfusion. [Am J Perinatol 2019;36:1332-1336]

A paper published in early 2022 outlined the limitations of gravimetric QBL during caesarean birth, pointing out that gravimetry overestimated blood loss in more than 80 percent of cases; in nearly 70 percent of patients, QBL differed from actual measured blood loss by more than 250 mL. [AJP Rep 2022;12:e36-e40]

Future studies that comprehensively assess QBL in high-risk and emergency deliveries, as well as in comparison with EBL and other alternative measurement methods, are needed to more definitively assess its clinical utility.