Fig. 4

Definition of the plans and the three pulling phases. a The first plane was defined by the lower border of the pubic symphysis and the coccyx. b The second plane was defined by the lower border of the pubic symphysis and the two sciatic spines. The crossing of these planes by the virtual point, presumed to coincide with the foetal cephalic presentation, defines the first phase (a: from the beginning of the traction until the passage of the first plane), the second phase (b: from the first plane until the passage of the second plane), and the third phase (c: from the second plane until traction stops)