OP18.07: Head progression in fetuses with persistent occiput posterior position at delivery: longitudinal assessment by 3D ultrasound in the second stage. - Maroni, E.; De Musso, F.; Giorgetta, F.; Nanni, M.; Youssef, A.; Contro, E.; Gabrielli, S.; Rizzo, N.; Pilu, G.; Ghi, T. (Ultrasound in Obstetrics & Gynecology, 2012)