Influence of previous delivery mode on perineal trauma risk

OBJECTIVE: To evaluate the impact of a previous pregnancy and delivery on perineal trauma rates in the subsequent vaginal birth. METHODS: Retrospective cohort study. The perineal outcomes of secundiparous women with history of previous (first) delivery in one of three categories: failed operative vaginal delivery (FOVD) and second‐stage emergency cesarean section (EmCS); elective cesarean section (ElCS), and vaginal delivery (VD) with intact perineum, were compared with a control primiparous group. RESULTS: The percentage obstetric anal sphincter injuries (OASIS)at first vaginal delivery was 17.3% (n = 9) after previous FOVD+EmCS, 12.9% (n = 18) after previous ElCS, and 0.6% (n = 9) after previous VD maintaining an intact perineum, compared with 6% (n = 1193) in the control primiparous group of women. Multivariate regression analysis demonstrated that previous FOVD+EmCS and ElCS were associated with a statistically significant increased risk of OASIS of 180% and 110% when compared with control (odds ratio [OR] 2.80; 95% confidence interval [CI] 1.35–5.78 and OR 2.10; 95% CI 1.27–3.48, respectively). Previous VD with intact perineum was associated with a statistically significantly reduced risk of OASIS (OR 0.09; 95% CI 0.04–0.17). CONCLUSIONS: Previous FOVD+EmCS and ElCS were associated with increased risk of OASIS in subsequent vaginal delivery compared with control, whereas previous VD with intact perineum was associated with decreased risk.