4、efaceandchin娩头时困难•theheadremainingtightlyappliedtothevulvaorevenretracting龟缩症•failure of restitution of the fetal head胎头没有自动复位和外旋转•failureoftheshoulderstodescend.肩没有下降(有宫缩的时候才会旋转下降)肩难产定义---•Shoulderdystociaisdefinedasadeliverythatrequiresadditionalobstetricmanoeuvrestoreleasetheshoulder