When the birth canal passes, the body of the fetus not only moves, but also adapts itself to the birth canal. Passing the pelvic ring and soft tissues - bends or unbends parts of the body. The entire complex of translational, flexural and extensor movements, which the fetus does in this case, is called the biomechanism of birth.
The lowest point, which is first born, is called the wire point, and the place by which the fruit rests for movement under the pubic symphysis-the fixation point. The biomechanism of childbirth depends on the presentation (what part of the fetus is above the entrance to the small pelvis), insertion (part of the fetus that has already entered and fixed in the small pelvis), the size and shape of both the pelvis and the head of the fetus.
Biomechanism of childbirth with head presentation
The presentation is normal in the head (the head is located above the entrance to the pelvis) and the gluteal (above the entrance - the buttocks of the fetus), oblique, transverse or leg presentation - this is not a variant of the norm and requires the intervention of a gynecologist and special tactics of labor. In the occipital presentation, the wired point will be the occiput. The front view is the one in which the back is turned to the front wall of the uterus, and at the back it is facing the back wall.
Biomechanism of labor with occipital presentation
1. At forward view:
- bending of the head (a small fontanel becomes the wire point);
- an inner turn of the head in the mother's pelvis, where the nape of the fetus moves to the symphysis, and the forehead to the mother's sacrum;
- extension of the head when passing under a laparar arc, where the fruit rests against the suboccipital part and the head unbends under this fixation point, passing in a small oblique size (9.5 cm);
- the outer turn of the head and the inner rotation of the shoulders, when the shoulders of their largest size pass in a transverse or oblique dimension, after passing the shoulders, all other parts of the fruit are quickly born.
2. In the back view:
- bending the head (the wire point is a small fontanel or a region between small and large);
- the inner turn of the head - the nape turns to the sacrum, and the forehead to the left articulation, the additional flexion of the head - during the eruption of the head, the frontal part of it rests against the lower edge of the symphysis - this is the first fixation point around which the head is bent, and the second is the suboccipital fossa, with which the fruit rests against the coccyx, extension occurs with the birth of the head;
- external turn of the head with an inner turn of the hangers.
Of other head presentations, births are possible with extensor (anterior and facial presentation), but in the frontal prognosis it can be extremely unfavorable and the mortality of newborns is very large - with a dense insertion, the birth of the fetus of the live fetus becomes impossible.
Biomechanism of labor with pelvic (breech) presentation
The variant of the norm is the breech presentation of the fetus, at which the child will be born by the pelvic end forward. Childbirth in this presentation is not a pathology, but they are more difficult.
Biomechanism with pelvic presentation:
- insertion of the gluteal part of the fetus in the small pelvis oblique in size, the wire point becomes one of the buttocks of the fetus;
- an internal turn of the buttocks in a straight size, after which one of the buttocks is facing the symphysis, the other - to the coccyx;
- lateral flexion of the trunk, in which the point of fixation of the buttock - under the lumbar arch, around it bends and the pelvic part is born;
- an internal turn of the shoulders with an external turn of the trunk, in which the shoulders of the fetus are located in a direct size;
- lateral flexion of the cervicothoracic region, in which the front shoulder is fixed under the bosom and the posterior shoulder is borne when flexed;
- the inner turn of the head, it turns the occiput forward, the suboccipitary fossa is fixed under the lone articulation and bent, being born in a bent position.
The leg presentation is similar to the pelvic presentation, but at the same time they try to avoid falling out of the legs and try to slow down their birth, trying to translate the leg presentation into the gluteal.