While engagement is an essential element of the cardinal movements, it can, and often does, happen before labor starts. Engagement of the fetal head is confirmed when the biparietal diameter of the vertex is at or past the level of the pelvic inlet. Station of the fetal head refers to where the biparietal diameter is in relation to the ischial spines of the maternal pelvis. The mechanical steps of the fetus in its passage through the birth canal are engagement, descent, flexion, internal rotation (most commonly, this is where the fetus rotates to the occiput-anterior position), extension, external rotation, and expulsion ( Fig. The cardinal movements of labor describe the movements a fetus goes through as it moves through the maternal pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. 1 The pear shape of the uterus, as well as the gynecoid shape of the maternal pelvic bones, positions the fetus in the vertex presentation in nearly 97% of deliveries. seven discrete cardinal movements of the fetus are described: engagement, descent, flexion, internal rotation, extension, external rotation or restitution, and expulsion Dr. Recent studies have posited that the surfactant molecule in the lungs of the fetus may play a role in parturition. CARDINAL MOVEMENTS IN LABOR Refer to the changes in position of fetal head during its passage through the birth canal. Following the onset of early labor, prostaglandins E2/F2-alpha, estrogen, and oxytocin coordinate to stimulate the myometrium, providing regular, rhythmic uterine contractions. As the uterus readies for labor over the course of days and weeks, the increased expression of prostaglandin and oxytocin receptors is upregulated, in addition to an increase in myometrial gap junction formation. ![]() Throughout pregnancy, true labor is held in check by inhibitors such as progesterone, prostaglandin I-2, relaxin, and nitrous oxide. ![]() The physiology of parturition is an orchestrated event involving many players-the myometrium, the decidua, and the uterine cervix. Anglo-American literature lists 7 cardinal movements, namely engagement, descent, flexion, internal rotation, extension, external rotation, and expulsion.
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