Supine position compared to other positions during the second stage of labor: a meta-analytic review. J Psychosom Obstet Gynaecol. 2004 Mar;25(1):35-45.

High quality meta-analysis comparing supine with other positions for the second stage of labor. The only significant results are, supine vs others : more instrumental deliveries and more episiotomies, more pain and less satisfaction. None of the foetal outcomes shows any significant difference.