The Inter-Rater Reliability and Agreement of a 0 to 10 Uterine Tone Score in Cesarean Delivery.

Abstract Background Postpartum hemorrhage is a leading source of maternal morbidity and mortality worldwide with uterine atony identified as the underlying cause in up to 80% of cases. Several measures have been utilized to report uterine tone. The most commonly reported measure is a 0-10 numerical rating scale, but this scale has not been tested for reliability or agreement between different raters. Objectives The primary purpose of this study was to evaluate the inter-rater reliability and agreement of the 0-10 visual numeric rating scale of uterine tone during cesarean delivery. A secondary purpose was to obtain estimates of scale responsiveness and minimal clinically important difference. Study Design Between August and November of 2018, obstetricians used a 0-10 numeric rating score to independently rate uterine tone at 3 and 10 minutes post-cesarean delivery by palpation of the uterus. ‘0’ represented ‘no tone’ and ‘10’ represented excellent tone. Each obstetrician independently and blinded to the other's score pointed to a numeric rating scale held by the anesthesiologist through a clear sterile drape. Intraclass correlation coefficients and Bland-Altman analysis were used to assess inter-rater reliability and agreement, respectively. Standardized response mean and standard error of measurement were used to obtain estimates of responsiveness and minimal clinically important difference, respectively. Results A total of 82 and 84 pairs of scores were collected at 3 and 10 minutes, respectively from pairs of 62 unique obstetricians. The mean ± standard deviation difference in scores between rater 1 and rater 2 was 0.4 ± 1.4 at 3 minutes and 0.1 ± 1.1 at 10 minutes. Intraclass correlation coefficients (95% confidence interval) for a future single rater (intraclass correlation coefficient [1,1]) at 3 and 10 minutes were 0.67 (0.53, 0.77) and 0.61 (0.46 0.73), and for the average between two future raters (intraclass correlation coefficient [1,2]) they were 0.80 (0.71, 0.87) and 0.76 (0.63, 0.84), indicating good and excellent reliability, respectively. Bland-Altman analysis estimated 95% limit of agreement between raters of -2.4 (95% confidence interval: -3.0, -1.9) to 3.1 (95% confidence interval: 2.6, 3.7) at 3 minutes and -2.1 (95% confidence interval: -2.5, -1.7) to 2.4 (95% confidence interval: 2.0, 2.8) at 10 minutes, consistent with good inter-rater agreement at both time points. The standardized response mean from 3 to 10 minutes post-delivery was 1.1 (n=81). Standard error of measurement (95% confidence interval) was 1.0 (0.9, 1.1) at 3 minutes and 0.8 (0.7, 0.9) at 10 minutes. Conclusions The 0-10 numeric rating scale for uterine tone demonstrated good to excellent inter-rater reliability with 1 and 2 raters, respectively, and good inter-rater agreement. The scale was responsive to within-parturient change in tone, and preliminary estimates of the minimal clinically important difference were obtained. The 0-10 numeric rating scale for uterine tone may be a reliable, standardized tool for future research in reporting degree of uterotonic contraction during cesarean delivery.