The Association Between Episiotomy and Obstetrical Anal Sphincter Injuries Among Vacuum-Assisted Vaginal Deliveries: A Population-Based Retrospective Canadian Cohort Study.

INTRODUCTION AND HYPOTHESIS: Vacuum-assisted vaginal deliveries (VAVD) represent a growing proportion of operative vaginal deliveries. Mediolateral episiotomy in patients undergoing VAVD has been shown to reduce obstetrical anal sphincter injuries (OASIS) in some settings; however, results of Canadian studies have been conflicted, and the practice has not been widely adopted by Canadian providers. The objective of this study was to estimate the association between episiotomy and OASIS among patients undergoing VAVD in a Canadian cohort.

METHODS

A population-based, retrospective cohort of patients who underwent VAVD at term of non-anomalous, singleton, vertex fetuses between 2005 and 2023 were identified using the  Nova Scotia Atlee Perinatal Database. Augmented inverse probability weighting analyses were used to estimate risk ratios (RR) with 95% confidence intervals (CI) adjusting for confounding variables, overall and stratified by length of the second stage of labour and parity.

RESULTS

Of 8407 VAVD, OASIS occurred in 970 (10.3%). Episiotomy was performed in 3780 (45.0%) VAVD. Overall, episiotomy was not found to be associated with OASIS risk (RR 0.94, 95% CI 0.83-1.07). Among individuals with a total second stage ≥ 60 min (RR 0.86, 95% CI 0.75-0.99) and an active phase ≥ 60 min (RR 0.60, 95% CI 0.34-1.06), episiotomy was associated with decreased OASIS risk. When stratified by parity, episiotomy was associated with reduced OASIS risk in nulliparous (RR 0.86, 95% CI 0.75-0.99) and increased risk in parous individuals (RR 1.37, 95% CI 0.99-1.90).

CONCLUSIONS

Among patients undergoing VAVD, episiotomy was protective against OASIS in certain populations, including nulliparous individuals and those with longer second stage of labour.