Vertex presentation with longitudinal lie:

While a transverse lie prior to labor can be manually versed to a longitudinal lie, once the uterus starts contracting the uterus normally will not allow any version procedure.

Shoulder presentations are uncommon (about 0.5% of births) as usually towards the end of gestation either the head or the buttocks start to enter the upper part of the pelvis anchoring the fetus in a longitudinal lie.

A cephalic 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).

It is not known in all cases of shoulder presentation why the longitudinal lie is not reached, but possible causes include bony abnormalities of the pelvis, uterine abnormalities such as malformations or tumors (fibroids), and other tumors in the pelvis or abdomen can also lead to a shoulder presentation.