![]() 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. ![]() 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. Recent studies have posited that the surfactant molecule in the lungs of the fetus may play a role in parturition. These are described in relation to a vertex. Following the onset of early labor, prostaglandins E2/F2-alpha, estrogen, and oxytocin coordinate to stimulate the myometrium, providing regular, rhythmic uterine contractions. The mechanisms of labor, also known as the cardinal movements, involve changes in the position of the fetus’s head during its passage in labor. Study with Quizlet and memorize flashcards containing terms like engangement, descent, flexion and more. posterior shoulder passes under the symphisis pubis. The CNM reports that the estimated fetal weight is 7 to 8 lb and the station is +3/5. She has been fully dilated for 3.5 hours and pushing for 2.5 hours with a Category 1 fetal heart rate tracing. allows the shoulders to rotate to fit in the pelvis, expulsion. The patient had a normal first stage of labor with placement of a combined spinal-epidural anesthetic at a cervical dilation of 4 cm. 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. fetal head passes the symphysis pubis, fetal head must change from attitude to flexion, external rotation. Happy Birthday little one Expulsion is the movement where the baby’s shoulders pass the pubic bone and delivered. 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.
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