Detailed classification of second-degree perineal tears in the delivery ward: an inter-rater agreement study

Second-degree perineal tears can vary widely as to the extent of trauma, which may be relevant for women's pelvic floor health postpartum. However, the short- and long-term consequences of second-degree perineal tears are poorly understood, likely due to the lack of a detailed classification system. Such a classification system for second-degree tears has been suggested but the inter-rater agreement has not yet been assessed. The aim of this study was to assess the inter-rater agreement of the already established classification system for perineal tears recommended by the Royal College of Obstetricians and Gynaecologists (RCOG classification) among midwives. Further, we aimed to assess the inter-rater agreement of a classification system that provides three sub-categories for second-degree perineal tears.

This was an inter-rater agreement study, conducted at Akershus University Hospital in Norway from 31 August to 29 November 2020. All midwives working in the delivery ward participated in the study. Midwives classified the integrity of the perineum of all women delivering vaginally within the study period. During the first month of the study, tears were classified by two midwives who were blinded to each other's findings, and the agreement of the RCOG classification was assessed. The following month, the detailed classification system was introduced to the midwifery staff. The last month, perineal tears were classified by two midwives using the detailed classification system, and the agreement was assessed. Inter-rater agreement was measured using Fleiss multirater kappa (k) and Kendall's coefficient of concordance (KCC_w ).

The inter-rater agreement for the RCOG classification was good to very good, with k = 0.705 (95% confidence interval [CI] 0.62-0.79, P < 0.001), KCC_w  = 0.928 (P < 0.001). The inter-rater agreement for the detailed classification system was good to very good, with k = 0.748 (95% CI 0.67-0.83, P < 0.001), KCC_w  = 0.956 (P < 0.001).

The inter-rater agreement among midwives using both the RCOG classification and the detailed classification system among midwives was good to very good. The detailed classification system provides additional information about the extent of tissue trauma in second-degree tears, warranted for future research on women's pelvic floor health postpartum.