RESUMEN
OBJECTIVE: This study describes the frequency of obstetric anal sphincter injuries (OASIS) in patients after instrumental delivery according to the type of forceps used. METHODS: A retrospective comparative cohort study was conducted on patients who underwent instrumental delivery from January 2017 to April 2022. The primary outcome was the presence of OASIS following delivery. Patients were categorized into Cohort A if only rotation forceps were used, Cohort B for only traction forceps, and Cohort C if both types were used sequentially. Statistical analysis was performed with SPSS (IBM, New York, NY) with χ2, Fisher's exact, and analysis of variance testing. A P-value <0.05 was considered significant. RESULTS: OASIS occurred in 45 of 328 instrumental deliveries. OASIS after rotation forceps occurred in 12.9% (n = 8) of cases, after traction forceps in 13.2% (n = 34), and after sequential use of rotation and traction forceps in 37.5% (n = 3) of cases (p = 0.141). An odds ratio (OR) of 0.91 (95% confidence interval [CI] 0.40-2.08) for OASIS was obtained with the use of rotation forceps, 0.81 (95% CI 0.38-1.70) for traction forceps, and 3.97 (95% CI 0.91-17.2) for the sequential use of rotation and traction forceps. CONCLUSION: There were no significant differences in the presence of OASIS comparing traction and rotation forceps. A non-significant trend of higher OASIS following the sequential use of traction and rotation forceps was observed.