In obstetrics, a cephalic presentation or head presentation or head-first presentation is a situation at childbirth where the fetus is in a longitudinal lie and the head enters the pelvis first; the most common form of cephalic presentation is the vertex presentation, where the occiput is the leading part (the part that first enters the birth canal). All other presentations are abnormal (malpresentations) and are either more difficult to deliver or not deliverable by natural means..