Is water delivery a good idea to prevent obstetric anal sphincter injuries in low risk primiparae? An exploratory study in a Swiss public teaching hospital.

• The rate of OASIS was compared in a big cohort of primiparae with "hands on" technique to protect the perineum in water and bed deliveries. • Secondary outcomes were the rate of OASIS in association with birth weight, episiotomies, and oxytocin during labor. • "Hands on" delivery in water without the use of oxytocin results in the lowest rates of obstetric anal sphincter injuries. Obstetric anal sphincter injuries are feared perineal injuries that are associated with increased pelvic floor disorders. The knowledge of influencing factors as the mode of delivery is therefore important. The aim of this study is to compare the rate of obstetric anal sphincter injuries in primiparae after water and bed deliveries. In this retrospective cohort study 3907 primiparae gave birth in water or on a bed in a Swiss teaching hospital. The diagnosis of obstetric anal sphincter injuries was confirmed by a consultant of obstetrics and gynecology and treated by them. The rates of these injuries after water and bed births were compared. Subgroup analysis was performed to detect possible associative factors, such as birth weight, episiotomy, use of oxytocin in first and second stage of labor. 1844 (47.2 %) of the primiparae had a water delivery and 2063 (52.8 %) a bed delivery. 193 (4.94 %) were diagnosed with obstetric anal sphincter injuries, of which 68 (3.7 %) had a water delivery and 125 (6.1 %) a bed delivery, p < 0.001. Subgroup analysis revealed that, in the first and second stage of labor, the rate of obstetric anal sphincter injuries with oxytocin was significantly lower in water than in bed deliveries; p = 0.025, p < 0.017, respectively. The rate of obstetric anal sphincter injuries in the birth weight or episiotomy subgroups did not reach significance. In a teaching hospital setting with standardized labor management, primiparae with a water delivery have the lowest risk for obstetric anal sphincter injuries. [ABSTRACT FROM AUTHOR]