As a result, a smaller structure emerges that can fit through the pelvis of the mother. FlexionĪs it passes through the pelvis, the fetal head flexes, bringing the chin into contact with the fetal chest. The two stages of labor's deceleration and the third stage are when falls occur at the highest rate. The process of the fetal descent is not steady or continuous. Descentĭescent describes the movement of the presenting component via the pelvis as it moves downhill. In nulliparous women, this typically occurs two to three weeks prior to labor, and in multiparous women, it may happen at any point before or after labor begins. Internal shoulder rotation and external head rotation lateral flexionĮngagement is the process by which the largest portion of the fetus passes through the pelvic inlet.The posterior portion of the anterior parietal bone is the portion that is visible.Īs the left occipito - anterior and occipito - lateral are the commonest, the mechanism of labor in such position is as follows:.One of the best flexions is the attitude.The occipitoanterior position is either right or left.The pubic bone will serve as the pivot point for whatever comes out of the pelvis.The part that leads and first encounters the pelvic floor's resistance will rotate forward until it passes under the symphysis pubis.The chin, mouth, nose, forehead and finally the occiput emerge.Definition: The term "labor mechanism" refers to the series of motions that the head undergoes during the adaptation process as it passes through the pelvis. This set of movements is observed as external rotation of the shoulder, with the fetal back facing upwards. However, if the chin becomes anterior, rotational dystocia will occur. Totally flexed, the head goes through an internal rotation motion to place the occiput under the symphysis. The anterior shoulder is wedged under the symphysis pubis at the level of the acromion, while the posterior shoulder pushes the coccyx backwards and is expelled, followed by expulsion of the anterior shoulder. The biacromial diameter then becomes anteroposterior, the fetal back points to the maternal right or left side, and the head begins to flex. The upper limbs are forced into flexion, shortening the biacromial diameter before assuming an oblique diameter. The abdomen and the most inferior portion of the fetal chest are expelled. In complete breech presentation, the lower limbs are usually expelled at the same time as the buttocks. The posterior buttock pushes the coccyx backwards, distends the perineum, and then becomes exteriorized, which fully releases the anterior buttock. The anterior buttock descends under the pubic bone and begins to open the vulvar orifice. In the anterior positions, a 45-degree backward rotation in the posterior positions, a 45-degree forward rotation occurs. The bitrochanteric diameter descends obliquely with slight posterior asynclitisim ( the posterior buttock descends ahead of the anterior buttock, the intergluteal cleft is closer to the pubis than to the sacrum).Įngagement usually occurs in an oblique position (left sacrum anterior, right sacrum anterior, left sacrum posterior, right sacrum posterior).Ī 45-degree internal (ie, in the birth canal ) rotation occurs.
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