In the sinicipital presentation the large fontanelle is the presenting part; with further labor the head will either flex or extend more so that in the end this presentation leads to a vertex or face presentation. In the brow presentation the head is slightly extended, but less than in the face presentation. The chin presentation is a variant of the face presentation with maximum extension of the head. Non-cephalic presentations are the breech presentation (3.5%) and the shoulder presentation (0.5%). Vertex presentation
The vertex is the area of the vault bounded anteriorly by the anterior fontanelle and the coronal suture, posteriorly by the posterior fontanelle and the lambdoid suture and laterally by 2 lines passing through the parietal eminences. In the vertex presentation the occiput typically is anterior and thus in an optimal position to negotiate the pelvic curve by extending the head. In an occiput posterior position, labor becomes prolonged, and more operative interventions are deemed necessary. The prevalence of the persistent occiput posterior is given as 4.7%.The vertex presentations are further classified according to the position of the occiput, both right, left, or transverse and anterior or posterior:

Left Occipito-Anterior (LOA), Left Occipito-Posterior (LOP), Left Occipito-Transverse (LOT)
Right Occipito-Anterior (ROA), Right Occipito-Posterior (ROP), Right Occipito-Transverse (ROT)The Occipito-Anterior position is ideal for birth; it means that the baby is lined up so as to fit through the pelvis as easily as possible. The baby is head down, facing the spine, with its back anterior.
For the Oskie position to occur the babys head must be far down the pelvis in order to allow room for leg extension, typically the arms are bent, tucked against the babys body. There are no known complications for labor and delivery. This presentation is rare and is not well researched. Reasons for predominance
The piriform (pear-shaped) morphology of the uterus has been given as the major cause for the finding that most singletons favor the cephalic presentation at term. The fundus is larger and thus a fetus will adapt its position so that the bulkier and more movable podalic pole makes use of it, while the head moves to the opposite site. Factors that influence this positioning include the gestational age (earlier in gestation breech presentations are more common as the head is relatively bigger), size of the head, malformations, amount of amniotic fluid, presence of multiple gestations, presence of tumors, and others. 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. Diagnosis
Usually performing the Leopold maneuvers will demonstrate the presentation and possibly the position of the fetus. Ultrasound examination delivers the precise diagnosis and may indicate possible causes of a malpresentation. On vaginal examination, the leading part of the fetus becomes identifiable after the amniotic sac has been broken and the head is descending in the pelvis. Management
Many factors determine the optimal way to deliver a baby.