Introduction and hypothesis: The aim of the mediolateral episiotomy incision is to increase the diameter of the soft tissue of the vaginal outlet to facilitate birth and to prevent vaginal tears. Episiotomy angles that are too narrow and close to the midline increase the risk of obstetric anal sphincter injuries. In order to determine the optimal angle of the episiotomy, we assessed the changes in the angles of episiotomy lines marked during the first stage of labor and measured at the time of crowning of the head.
Methods: Incision lines for mediolateral episiotomy were marked on the perineal skin at angles of 30°, 45°, and 60° from the midline during the first stage of labor in women with a singleton pregnancy. The angles of the marked lines were measured at crowning of the head. Mediolateral episiotomy was performed only for obstetric indications.
Results: The study included 102 women with a singleton pregnancy. Of these women, 50 were primiparous and 52 were multiparous. All angles marked during the first stage of labor increased significantly (by more than 30°) at crowning of the head. Similar changes were observed in primiparous and multiparous women.
Conclusions: The angle of the mediolateral episiotomy line was significantly greater at crowning of the head than when marked during the first stage of labor. To achieve the desired episiotomy angle, it is important to take into consideration the changes in mediolateral episiotomy angles that occur during labor.
Keywords: Crowning; Incision angle; Mediolateral episiotomy.