Of the neck so that the smallest diameter possible presents. If the neck does not flex, it may actually extend during labor, producing a brow or face presentation. Progressive with thinning of the cervix and lower uterine segment. Depends on the force of contractions and on pelvic and presenting part configuration. Occurs during descent.
Vertex rotates from transverse to either posterior or anterior position to pass the ischial spines.
Occurs as the head distends the perineum and the occiput passes beneath the symphysis. Occurs after delivery of the head with the head rotating back to a transverse position as the shoulders internally rotate to an anteroposterior position. Management of vertex delivery. Preparations for delivery. Should be made when the presenting part begins to distend the perineum, sooner for multigravida.