Obstetrical situations with a high risk of anal sphincter laceration in vacuum-assisted deliveries

Objective. To determine risk factors for anal sphincter laceration and define situations with a high risk for such trauma in vacuum-assisted deliveries. Design. Retrospective observational study of 1961 vacuum-assisted deliveries over a period of 5 years. Setting. French university hospital. Population. All women who delivered with vacuum assistance. Methods. Third- and fourth-degree perineal tears were reviewed. The factors studied through univariate and multivariate logistic regression were the mother's age, parity, history of assisted delivery, cesarean section, gestational age, uterine fundal height, duration of the second stage of labor, head position at expulsion, epidural anesthesia, episiotomy, biparietal diameter and birthweight. Main outcome measures. Third- and fourth-degree perineal tears. Results. There were 1.9% third-degree and no fourth-degree perineal tears. Risk factors identified were occipito-posterior position (odds ratio 4.7, p < 0.001), biparietal diameter (odds ratio 2.0 for each 5 mm increase, p= 0.004), duration of second stage (only significant when parity was =1; odds ratio 1.3 for each 10 min increase, p= 0.004) and nulliparity (decreasing effect according to duration of the second stage). The patterns of the association between these factors and the risk of perineal tears were different for nulli- and multiparous women. Conclusions. In a targeted population of women having vacuum-assisted deliveries, the association of specific risk factors allows clinicians to identify women who are at high risk of anal sphincter laceration.