The Association of Episiotomy with Obstetric Anal Sphincter Injury-A Population Based Matched Cohort Study

• Authors: Sari Raisanen, Emory University; Tuomas Selander, Kuopio University Hospital; Rufus Cartwright, Imperial College London; Mika Gissler, Nordic School of Public Health; Michael Kramer, Emory University; Katariina Laine, University of Oslo; Seppo Heinonen, Kuopio University Hospital
• Journal Title: PLoS ONE
• Volume: Volume 9, Number 9
• Publisher: Public Library of Science | 2014-09-09, Pages e107053-e107053
• Type of Work: Article | Final Publisher PDF
• Publisher DOI: http://doi.org/10.1371/journal.pone.0107053
• Subjects: Health Sciences, Epidemiology; Health Sciences, Medicine and Surgery
• Keywords: Science & Technology; Multidisciplinary Sciences; Science & Technology - Other Topics; RANDOMIZED CONTROLLED-TRIAL; OPERATIVE VAGINAL DELIVERY; RISK-FACTORS; ROUTINE; REGISTER; QUALITY; WOMEN

Abstract

Objectives:To estimate the independent association of episiotomy with obstetric anal sphincter injuries (OASIS) using first a cross-sectional and then a matched pair analysis. Design: A matched cohort. Setting: Data was gathered from the Finnish Medical Birth Register from 2004-2011. Population: All singleton vaginal births (n = 303,758). Methods: Women resulting matched pairs (n = 63,925) were matched based on baseline risk of OASIS defined based on parity (first or second/subsequent vaginal births), age, birth weight, mode of delivery, prior caesarean section, and length of active second stage of birth. Results: In cross-sectional analysis episiotomy was associated with a 12% lower incidence of OASIS (adjusted odds ratio (aOR) 0.88, 95% confidence interval (CI) 0.80 to 0.98) in first vaginal births and with a 132% increased incidence of OASIS in second or subsequent vaginal births (aOR 2.32, 95% CI 1.77 to 3.03). In matched pair analysis episiotomy was associated with a 23% (aOR 0.77, 95% CI 0.69 to 0.86) lower incidence of OASIS in first vaginal births and a 61% (aOR 1.61, 95% CI 1.14 to 2.29) increased incidence of OASIS in second or subsequent vaginal births compared to women who gave birth without an episiotomy. The matched pair analysis showed a 12.5% and a 31.6% reduction in aORs of OASIS associated with episiotomy, respectively. Conclusions: A matched pair analysis showed a substantial reduction in the aORs of OASIS with episiotomy, due to confounding by indication. This indicates that results of observational studies evaluating an association between episiotomy and OASIS should be interpreted with caution.