In the vertex presentation the occiput typically is anterior and thus in an optimal position to negotiate the pelvic curve by extending the head.
2.
A "'malpresentation "'is any presentation other than a vertex presentation ( with the top of the head first ).
3.
Two-thirds of all vertex presentations are LOA, possibly because of the asymmetry created by the descending colon that is on the left side of the pelvis.
4.
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 ).
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