The biomechanism of childbirth is a whole set of different movements that the fetus makes passing through the birth canal. These movements are directly related to the structure of the female pelvis. They consist in flexion / extension of the baby's head, its rotation around the axis, lateral inclination of the fetal head and pendulum movements aimed at its advancement along the birth canal.
All these movements are provided by the size and shape of the woman's pelvis, the presence of sufficient amniotic fluid, the cheese-like lubricant that reduces friction on the baby's body, as well as the size and shape of the fetal head. In addition, the biomechanism of childbirth is provided by the activity of the uterus, more precisely, by its contractions. This creates translational movements to move the fetus along the maternal birth canal. An additional factor that contributes to the contraction of the uterus is its ligamentous apparatus. In this case, the round ligaments tighten the uterine fundus in front, and the sacraluterine - hold, not allowing to deviate, and fix it at the surface of the sacrum.
The biomechanism of labor in cephalic presentation of the fetus (occipital) consists of the following points: head flexion and its smooth lowering into the pelvic cavity. When the head is bent, the leading point is determined - a small fontanel, which approaches the wire line of the pelvis. It is this point that appears first from the genital gap. The chin of the fetus tends to the chest. At the beginning, the head changes its configuration. Further, when moving from the wide to the narrow part of the small pelvis, it makes a coup. After that, the face is directed to the sacrum, and the back of the head to the symphysis. And in conclusion, the head is unbent and leaves the plane of the pelvis - the forehead, face and last chin are born. After birth, the head takes its original position. Next, the shoulders are born and the fetus is completely expelled.
The biomechanism of labor in breech presentation also consists of rotational and translational movements, only in this case the fetus passes through the birth canal with the pelvis forward. In this case, the main reference point is the intertrochanteric gluteal line. The following moments are distinguished that make up the biomechanism of childbirth: the buttocks are inserted into the small pelvis and move along it, the fetal spine makes a lateral bend, after which the torso and shoulder girdle are born. Flexion of the fetal head and its internal rotation occur almost simultaneously. The head is born in a bent position.
The biomechanism of labor with a foot presentation is similar to thatwhich is observed in the gluteus. Often, after all the amniotic fluid has drained, and with the cervix still incompletely dilated, the presenting leg may descend and even fall out of the vagina. This significantly complicates and delays the course of childbirth. After the cervix opens completely, the buttocks appear immediately behind the leg, and so on according to the above biomechanism of childbirth.
As you can see, the biomechanism of natural birth depends on the position of the fetus and the placement of the wire point.
