cardinal movements of labor

cardinal movements of labor,

the typical sequence of positions assumed by the fetus as it descends through the pelvis during labor and delivery. The positions are usually designated as engagement, flexion, descent, internal rotation, extension, external rotation or restitution, and expulsion. The birth canal is a curved cylinder; the head must enter it in a downward, transverse direction but exit it in a more forward, anteroposterior direction. In a vertex presentation, engagement of the head in the pelvic inlet requires that it have flexion with the chin on the chest. After descent the head must undergo extension to turn forward and be born under the symphysis. The pelvic inlet is heart-shaped, and the fetal head enters it facing obliquely. However, the pelvic outlet is diamond-shaped, and the head usually exits it facing posteriorly and must undergo internal rotation to do so. After delivery of the head, the shoulders remain for a time in the oblique plane, and the head undergoes external rotation or restitution to allow the widest diameter of the shoulders to be delivered from the longer anteroposterior diameter of the pelvic outlet.