Cephalic presentation is the most common and can be further subclassified as vertex, sinciput, brow, face, and chin. The presentation can roughly be divided into the following classifications: cephalic, breech, shoulder, and compound. The anterior shoulder rotates under the symphysis pubis, after which the rest of the body usually delivers without difficulty.The term presentation describes the leading part of the fetus or the anatomical structure closest to the maternal pelvic inlet during labor. After delivery of the head and external rotation, further descent brings the anterior shoulder to the level of the symphysis pubis. This is again a passive movement resulting from a release of the forces exerted on the fetal head by the maternal bony pelvis and its musculature and mediated by the basal tone of the fetal musculature.Įxpulsion: Expulsion refers to delivery of the body of the fetus. The forces responsible for this motion are the downward force exerted on the fetus by uterine contractions and maternal expulsive efforts along with the upward forces exerted by the muscles of the pelvic floor.Įxternal Rotation: After the fetal head deflexes (extends), it rotates to the correct anatomic position in relation to the fetal torso left or right rotation depends on the orientation of the fetus. The fetal head is delivered by extension and rotates around the symphysis pubis. At this point, the birth canal curves upwards. This descent brings the base of the occiput into contact with the inferior margin of the symphysis pubis. As with flexion, internal rotation is a passive movement resulting from the shape of the pelvis and the resistance of the pelvic floor musculature.Įxtension: Extension occurs once the fetus has descended to the level of the introitus. Internal Rotation: Internal rotation is the rotation of the presenting part from its original position (usually transverse with regard to the birth canal) to the anteroposterior position as it passes through the pelvis. The fetal position remains occiput transverse. When flexion occurs, the occipital (posterior) fontanel slides into the center of the birth canal and the anterior fontanel becomes more remote and difficult to feel. This functionally creates a smaller structure to pass through the maternal pelvis. The greatest rate of descent occurs during the deceleration phase of the first stage and during the second stage of labor.įlexion: While descending through the pelvis, the fetal head flexes so that the fetal chin is touching the fetal chest. Descent of the fetus is not a steady, continuous process. This normally occurs 2-3 weeks before labour in nulliparous women and may occur any time before or after onset of labour in multiparous women.ĭescent: Descent refers to the downward passage of the presenting part through the pelvis. Seven discrete cardinal movements of the fetus occur over the course of labor and delivery: engagement, descent, flexion, internal rotation, extension, external rotation or restitution, and expulsion.Įngagement: Engagement is the descent of the widest part of the fetus through the pelvic inlet. This is required for fetal descent through the birth canal. To accommodate itself to the maternal pelvic dimensions, the fetus must undergo a series of changes in the attitude of its presenting part.
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