Women who gave birth in the dorsal position were most likely to have a spontaneous second-degree tear. However, relationships are complex. For example, the lithotomy position is more likely to be used when an episiotomy is anticipated. First-time mothers were more likely to have an episiotomy, but the association disappeared when birth position was factored in because they were more likely to give birth in the lithotomy position. Attendant's experience may also be a factor.
Maternal position is related to perineal outcome only when student midwives attend the birth.
More research is needed. Legino LJ et al. 50 years' experience at a university hospital. Association of episiotomy and delivery position with deep perineal laceration during spontaneous delivery in nulliparous women. The study group was 241 nulliparous women having spontaneous, vertex, singleton births.