At the end of pregnancy and the beginning of labor, the buttocks of the fetus stand with their transverse dimension in one of the oblique sizes of the entrance to the small pelvis.
The first moment is - decrease in the volume of the hips and insert them into the plane of entry into the small pelvis. The lateral size of the buttocks (linea inter trochanterica) becomes in one of the oblique dimensions of the plane of entry into the small pelvis. At an oblique size, they descend into the pelvic cavity in such a way that the anterior buttock is below the posterior and plays the role of a leading point.
The second moment is - Inner turn of buttocks. Buttocks that perform an internal turn during the transition from the wide part of the small pelvis to the narrow one and end in the plane of exit from the small pelvis. They are set in a direct exit size: the front buttock approaches the lone articulation, and Zand to the coccyx.
The third moment is - lateral flexion of the lumbar spine. The iliac bone of the fetus (fixation point) is aligned with the mother's pelvis in the lumbar artery, with a significant lateral flexion of the lumbar part of the fetal spine and the birth of the posterior buttock. Then the arch of the spine becomes aligned and the anterior buttock is born.
The fourth moment is - an internal turn of the shoulders and an external turn of the trunk. Shoulders with their transverse size of the pelvis entering the oblique (through which the buttocks passed), and in the pelvic outlet they are set in a direct size, the fore shoulder is fixed by the symphysis (acromial process), the posterior one is returned to the coccyx.
The fifth moment is - lateral flexions of the cervicothoracic spine are the result of the formation of a fixation point between the lower edge of the lumbar arch and the site of attachment of the deltoid muscle. The trunk of the fetus bends in the cervico-thoracic region, with the back shoulder being born. Then the ridge is leveled and the front shoulder, shoulder girdle, and fetal handles are born.
The sixth moment is - internal rotation of the head. The head is in a bent state. Entering a strilopodimin suture in the oblique pelvic size (opposite to that through which the buttocks and shoulders passed). In the pelvic cavity, it gradually returns with an arrow-shaped suture into a straight dimension of the exit plane, as a result of which the nape is returned to the lone articulation and the face to the coccyx.
The seventh moment is - zginnannya heads. In the suboccipital fossa, the head rests against the pubic arch (the second fixation point) and begins to be coded. First appears bidborindya, then face, forehead, crown and head. The head is cut by a circle corresponding to its small oblique size.
There are 4 stages of clinical course of labor with pelvic presentation:
- Birth of the fetus before the navel;
- Birth of the fetus to the lower angle of the anterior scapula;
- Birth of the shoulder girdle;
- Birth of the fetal head.