Uterine tone numeric rating score as an early indicator of major postpartum hemorrhage during cesarean delivery: A prospective observational study.

BACKGROUND Postpartum hemorrhage (PPH) is the leading preventable cause of maternal mortality. Most PPH cases are caused by uterine atony, which is inconsistently defined in clinical care. We used the electronic health record (EHR) to prompt communication between the anesthesia and obstetric care teams about uterine tone using a validated 11-point numeric rating scale (NRS) at 0, 5, and 10-minutes after placental delivery for all cesarean deliveries (CDs) at our institution. Our primary hypothesis was that lower uterine tone NRS would be strongly associated with progression to major PPH. METHODS This was a single-center, prospective observational study conducted over a one-year period. The primary predictor was the 0-10 uterine tone NRS recorded 10-minutes after placental delivery, and the primary outcome was major PPH, defined as quantitative blood loss (QBL) ≥ 1,500 mL. Area under the receiver operating characteristic (AUROC) curves were created, and relative risk of major PPH for each one-point change in the tone score estimated. Key secondary outcomes analyzed included associations between tone scores, PPH, and blood transfusion. RESULTS 1,599 consecutive CDs were performed by obstetricians from academic (39.3%), county public health (21.1%), and private practice (38.8%) services. Major PPH complicated 9.9% and transfusion 6.7% of CDs. Uterine tone NRS was documented at 0-minutes after placental delivery in 91.6%, 5-minutes in 97.4%, and 10-minutes in 97.0% of CDs. The 10-minute NRS was a strong predictor of major PPH, with an AUROC of 0.78 (95% CI 0.73-0.82). Each one-point decrease in NRS increased the risk of major PPH by 71% (95% CI 0.58-0.86). A 10-minute uterine tone NRS ≤ 6 had high positive predictive value for major PPH (32.9%) as well as PPH (64.2%) and transfusion (20.6%). CONCLUSIONS Standardized uterine tone assessments on a 0-10 scale are feasible to implement and strongly associated with progression to major PPH and blood transfusion. Future studies should investigate whether implementation of PPH interventions based on uterine tone NRS can reduce major PPH and hemorrhage-associated morbidity.