[Eutocic delivery ].

Delivery is uncomplicated in 60 to 75% of cases. Movement through the pelvic pathway requires precise foetal mobility in relation to the pelvis, since the head must pass using a double rotation: 120 degrees deflection around the symphysis pubis and 45 degrees to 135 degrees rotation around the pelvic cavity, according to the presentation. This mechanism, imposed by the adaptation of the form of the pelvis to the upright position, is possible cue to an apparent reduction in volume of the foetal head by its molding and its flexion. This accommodation is favoured by the maturity of the foetal nervous system, the maturity of the uterus, and by the type of presentation. Anterior presentation (anterior left occipito-iliac), more common in multiparas, is usually safer than posterior presentation (posterior right occipito-iliac). more often seen in primiparas.