Another passive movement, this one is regulated by the basal tone of the fetal musculature and results from the release of forces placed on the fetal head by the mother's bony pelvis and its musculature. External RotationĪfter responding (expanding), the fetal head rotates to the proper anatomic position in relation to the fetal torso the rotation is to the left or right depending on the orientation of the fetus. When the uterus contracts after the head is born, this should take place. The anterior shoulder rotates forward when it reaches the right side of the pelvic floor, placing the shoulders inside the anteroposterior diameter of the exit. In LOA, the shoulder is in the left oblique diameter of the pelvic cavity. This motion resembles an internal head rotation. She can deliver the baby on her shoulder more easily without injuring her perineum. The occiput then points to the maternal thigh on the opposite side from where it originally rested. This movement indicates whether the position is right or left, and lets the midwife know whether she is giving birth to an LOA or a ROA. When an internal rotation occurs, the occiput of a vertex, LOA, returns 1/8th of a circle to the left. The neck twist brought on by internal head rotation is reversed by the visibly passive movements of the head. The pelvic floor muscles' upward forces and the downward forces applied to the fetus by uterine contractions and maternal expulsive efforts are what propel the motion. During extension, the fetal head emerges and revolves around the pubis symphysis. At this moment, the birth canal slopes upward. This fall brings the base of the occiput into contact with the inferior border of the symphysis pubis. ExtensionĮxtension happens when the fetus reaches the introitus' level. Crowning of the HeadĪfter the discomfort episode has passed, the head is termed to have crowned when it enlarges the vaginal opening without receding into the vagina. Similar to flexion, internal rotation is a passive motion brought on by the shape of the pelvis and the pelvic floor muscles' resistance. Internal rotation is the rotation of the presenting component from its initial position-typically transverse in relation to the birth canal-to the anteroposterior position as it moves through the pelvis. Transverse occiput remains the fetal posture. The anterior fontanel gets further away and more challenging to feel as the occipital (posterior) fontanel creeps into the birth canal. 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.
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