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Lesson 10: Fetal Positions and Adaptations |
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10-3. FETAL ADAPTATIONS (OR THE MECHANISM OF LABOR) a. Cardinal Movements. This refers to the movements made by the fetus during the first and second stage of labor. As the force of the uterine contractions stimulates effacement and dilatation of the cervix, the fetus moves toward the cervix. When the presenting part reaches the pelvic bones, it must make adjustments to pass through the pelvis and down the birth canal (see figure 10-6).
Figure 10-6. The mechanism of labor in the left occiput anterior (LOA) presentation. b. Fetus in the Vertex Position. The fetus in the vertex position makes seven adaptations or cardinal movements. Refer to figure 10-6.LOA or LOT, rotation is only a short distance-45 to 90 degrees. (c) If the head is in a posterior position, it may mean a turn of 180 degrees. (d) Occasionally, the fetus may not turn to the anterior position and is born O.P. (occiput posterior). (5) Extension. As the previously flexed head slips out from under the pubic bone, the fetus is forced to extend his head so that the head is born pushing upward out of the vaginal canal. The natural curve of the lower pelvis and the baby's head being pushed outward forces distention of the perineum and vagina. As it moves through the vaginal canal, the chin lifts up (extends) and the head is delivered. During this maneuver, the fetal spine is no longer flexed, but extends to accommodate the body to the contour of the birth canal.
c. Movement. The first four movements (descent, flexion, engagement, and internal rotation) do not have to occur in any specific order.A general understanding of how the fetus may present itself during labor will help you to understand why some labors are so long and difficult. In addition, this will help you in understanding what the fetus must go through during the process of presenting himself out of the patient's womb.
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