Trigonometric characteristics of episiotomy and risks for obstetric anal sphincter injuries in operative vaginal delivery.

ABSTRACT

INTRODUCTION AND HYPOTHESIS: The objective of this study was to investigate the association between the trigonometric properties of episiotomy in operative vaginal delivery (OVD) and obstetric anal sphincter injuries (OASIS). METHODS: The study included 72 primiparous women who had an OVD and episiotomy. Cases (n = 36) had sustained OASIS at birth, while controls (n = 36) had not. The groups were matched for instrumental delivery. The episiotomy scar was identified and its trigonometric characteristics were measured at 8-12 weeks postpartum. Data were analysed using conditional logistic analysis. RESULTS: The angle of episiotomy behaves as a factor associated with anal sphincter injury, so women with a mediolateral episiotomy and an angle greater than 20° have an 87% less risk of having an OASIS (odds ratio 0.13, 95% confidence interval 0.03-0.58). The study showed that scarred episiotomies at 8-12 weeks after OVD with an angle ≤ 20°, depth and distance between the episiotomy and anus ≤ 15 mm, total upper triangle perimeter ≤ 75 mm, para-anal triangle perimeter ≤ 15 mm and areas between scar and midline ≤ 250 mm(2) were significantly associated with higher risk of OASIS. CONCLUSIONS: When a mediolateral episiotomy is performed in OVD the technique has a strong effect on the occurrence of OASIS. Additional research is needed to determine if the optimal technique for mediolateral episiotomies produces less OASIS than deferring the performance of episiotomy.