Objective: To investigate whether episiotomy prevents 3rd or 4th degree perineal tears in critical conditions such as shoulder dystocia, instrumental deliveries (vacuum or forceps), persistent occiput-posterior position, fetal macrosomia (>4,000 g), and non-reassuring fetal heart rate (NRFHR) patterns.
Methods: A retrospective study comparing 3rd and 4th degree perineal tears during vaginal deliveries with or without episiotomy, in selected critical conditions was performed. Multiple gestations, preterm deliveries (<37 weeks' gestation) and cesarean deliveries were excluded from the analysis. Stratified analysis (using the Mantel-Haenszel technique) was used to obtain the weighted odds ratio (OR), while controlling for these variables.
Results: During the study period, there were 168,077 singleton vaginal deliveries. Of those, 188 (0.1%) had 3rd or 4th degree perineal tears. Vaginal deliveries with episiotomy had statistically significant higher rates of 3rd or 4th degree perineal tears than those without episiotomy (0.2 vs. 0.1%; P<0.001). The association between episiotomy and severe perineal tears remained significant even in the critical conditions. Stratified analysis revealed that the adjusted ORs for 3rd or 4th degree perineal tears in these critical conditions (Macrosomia OR=2.3; instrumental deliveries OR=1.8; NRFHR patterns OR=2.1; occipito-posterior position OR=2.3; and shoulder dystocia OR=2.3) were similar to the crude OR (OR=2.3).
Conclusions: Mediolateral episiotomy is an independent risk factor for 3rd or 4th degree perineal tears, even in critical conditions such as shoulder dystocia, instrumental deliveries, occiput-posterior position, fetal macrosomia, and NRFHR. Prophylactic use of episiotomy in these conditions does not seem beneficial if performed to prevent 3rd or 4th degree perineal tears.