Darbois Y
Service de chirurgie gynécologique et obstétrique Groupe hospitalier La Pitié-La Salpêtrière, Paris.
Rev Prat. 1999 Jan 15;49(2):133-8.
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.
60%至75%的分娩过程并无并发症。胎儿通过骨盆通道时，需要与骨盆保持精确的活动度，因为胎儿头部必须通过两次旋转才能通过：根据胎位，先围绕耻骨联合偏转120度，然后围绕盆腔旋转45度至135度。由于骨盆形态适应直立姿势，这种机制得以实现，这可能是由于胎儿头部通过塑形和屈曲，其体积明显减小。胎儿神经系统的成熟、子宫的成熟以及胎位类型都有利于这种适应性变化。前位胎位（左枕前位）在经产妇中更为常见，通常比后位胎位（右枕后位）更安全，后位胎位在初产妇中更为常见。
