The role of mediolateral episiotomy during labour. Analysis of risk factors for obstetric anal sphincter tears

Abstract

BACKGROUND: To determine risk factors for third-degree and complete third- or fourth-degree anal sphincter tears in vaginal delivery. METHODS: This is a retrospective comparative study. Fifty-three women who had sustained an anal sphincter tear were compared with 9,178 women without such a complication between August 1997 and October 2001. Obstetric data was collected from an electronic database. The main outcome measures were odds ratios. RESULTS: In the whole study population, odds ratios (ORs) for third-degree tears were: primiparity, 8.34 (95% confidence interval [CI] 3.98-17.48); vacuum extraction, 5.22 (95% CI 2.69-10.13); parietal presentation, 3.97 (95% CI 1.16-13.64); and birth weight >4,000 g, 3.77 (95% CI 2.11-6.68); and for complete third- or fourth-degree tears odds ratios were 5.42, 2.98, 5.64, and 3.01, respectively. In multivariate analysis, mediolateral episiotomy appeared to be protective as regards third-degree tears (OR 0.37 [95% CI 0.2020-0.70]). CONCLUSIONS: Vacuum-assisted vaginal delivery bears an increased risk of third-degree anal sphincter tears in a maternity unit where forceps are not used. Restricted use of mediolateral episiotomy may have a protective effect on the perineum.