Defining 'obstetric haemorrhage': Blood loss volume and severe morbidity.

Aims And Objectives: Our goal is to describe the association between total quantitative blood loss (QBL) and risk of obstetric haemorrhage-related morbidity (OBH-M) to assess the utility of the current definition of obstetric haemorrhage (OBH).

Methods: This was a retrospective cohort study completed of all patients who had a live delivery at the only urban safety-net hospital over a 2-year period from 2018 to 2019. We categorized deliveries into 10 equally sized deciles based on QBL and compared the proportion with OBH-M in each. Among the two deciles with the highest proportions of OBH-M, we stratified deliveries into seven groups of ascending intervals of 250cc QBL. Finally, we compared the positive predictive value (PPV) of the standard definition of OBH (QBL ≥ 1000cc) to a definition extrapolated from our stratified analysis. The primary outcome was proportion of deliveries within each QBL decile affected by OBH-M. The secondary outcome was PPV.

Results: We found a significant increase in OBH-M from decile 9 (895-1201cc QBL) to decile 10 (1205-8325cc QBL) (p < 0.001). In our stratified analysis, we found QBL of 1500cc to be an inflection point for an increased proportion of OBH-M. Our secondary analysis showed an increased PPV for OBH-M using QBL of 1500cc (20.5%) compared with that of QBL 1000cc (9.8%).

Conclusions: Our findings suggest that a higher QBL threshold than the currently accepted definition of OBH is more predictive of OBH-M.