The back view of the occipital presentation is a variant of the basic mechanism of delivery. When the occiput is located from behind, in most cases, the fetal head, describing the arch in 1350 returns backwards under the bony arch. In this case, the sagittal seam, which is in one of the oblique pelvic sizes, depending on the position (at the first - in the left, at the second - in the right), first passes into a transverse dimension, then in the opposite oblique, at the end in a straight line. If the turn of the occiput does not occur, the delivery takes place in the posterior form of the occipital presentation.
The first moment is - Folding and lowering of the fetal head. From the very beginning, there is a strong bending of the head. The leading point is the middle between the large and small fontanel. The swept suture becomes transverse or slightly oblique.
The second moment is - internal rotation of the fetal head. The sagittal seam, describing a small arc 450 goes into a direct dimension of the pelvic outlet, the back of the head, and accordingly, a small fontanelle, returns the sacrum, and the large one - to the chest.
The third moment is - additional bending of the head. The fetal head rests against the lower edge of the symphysis by the portion of the anterior margin of the hair that is the point of fixation, it is additionally bent, thus the parietal mounds and the occipital part of the head are born.
The fourth moment is - Extension of the head occurs as a result of the formation of a new fixation point between the suboccipital fossa and the tip of the sacrum. The head is born by a moderate extension, from under the symphysis the anterior margin of the head, forehead and face is born. Thus, the head is born face forward, the average oblique size - 10cm, in a circle - 33cm.
The fifth moment is - the inner turn of the trunk and the external turn of the head passes the same way as in the anterior occipital presentation. The configuration of the head in the posterior form of the occipital presentation is dolichocephalic.