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What initiates the withdrawal of progesterone before labor begins?
Which hormone is primarily released in response to pressure on the cervix during labor?
What is the role of prostaglandins in the initiation of labor?
What change in hormone ratio is interpreted as a sign of labor onset?
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Which of the following is a sign of true labor?
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How would you characterize Braxton Hicks contractions?
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What physiological change occurs to the cervix at term, signaling the approach of labor?
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What triggers contractions at a set point due to placental age?
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What does fetal attitude primarily describe?
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Which pelvic measurement indicates the narrowest diameter at the inlet?
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How does the fetal position facilitate birth?
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What is one of the key adaptations of the fetus in a normal fetal position?
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Which part of the fetus is mentioned as being flexed and folded on the chest?
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What is the role of the transverse diameter at the pelvic outlet?
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Which of the following describes a fetus in complete flexion?
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Which of the following does not represent a benefit of the fetal position?
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What is typically the presenting part of the fetus during labor?
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What occurs as the occiput is born during the labor process?
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Which movement is described as occurring almost immediately after the head of the infant is born?
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What helps the fetus maintain the smallest diameter of the head presenting to the pelvis?
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Which position does the head rotate to after passing through the birth canal?
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What is the effect of the head's external rotation on the shoulders?
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Which part of the fetus is primarily involved in the mechanism of labor?
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What does the term 'engagement' refer to in fetal positioning?
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What happens to the fetal head during the labor process after it is engaged?
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Which part of the fetus typically has the widest diameter?
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When is a fetus considered to be in moderate flexion?
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What does 'station' indicate in relation to a fetus?
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What is the most common type of fetal presentation during childbirth?
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Which term describes a change in the shape of the fetal skull due to uterine contractions?
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What defines the 'fetal lie'?
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What does partial extension of the fetus present during childbirth?
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What position should the fetal head take during descent into the pelvis?
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What is the primary concern if a woman bears down with her abdominal muscles too early during labor?
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What are the three phases of a uterine contraction?
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What does effacement refer to in the context of cervical changes during labor?
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During which phase of contraction is the intensity at its strongest?
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What movement occurs as the fetal head touches the pelvic floor?
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What is the normal length of the cervical canal before effacement?
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What facilitates the innermost rotation of the fetal head during labor?
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Study Notes
Theories of Labor Onset
- Labor typically begins when a fetus is sufficiently mature to survive outside the womb, but not too large for a safe birth
- Several factors, both fetal and maternal, contribute to labor initiation
- Increased uterine stretching triggers prostaglandin release, contributing to pain sensations
- Pressure on the cervix stimulates oxytocin production from the pituitary gland
- Rising estrogen levels relative to progesterone, interpreted as progesterone withdrawal, contribute to labor onset
- Placental age triggers contractions at a predetermined point
Passage: Pelvic Structure
- The passage refers to the route a fetus takes through the uterus, cervix, vagina, and perineum
- Two key pelvic measurements assess adequacy: diagonal conjugate (anteroposterior diameter of the inlet) and transverse diameter of the outlet
- At the pelvic inlet, the anteroposterior diameter is the narrowest point; at the outlet, the transverse diameter is the narrowest
Passenger: Anatomy and Position
- The passenger is the fetus, with the head being the widest part, making it potentially difficult for passage
- Molding refers to the reshaping of the fetal skull by uterine contractions during labor
- Engagement occurs when the presenting part of a fetus settles into the pelvis at the level of the ischial spines, indicating an adequate pelvic size
- Station describes the relationship of the presenting part to the ischial spines; 0 station means the part is at the level of the spines
- Fetal lie relates the fetal long axis to the maternal long axis; longitudinal (vertical) or transverse (horizontal)
- Fetal attitude refers to the degree of flexion a fetus assumes during labor
- Fetal presentation identifies the body part that first contacts the cervix; usually cephalic (head first), but can also be breech (buttocks or feet first) or shoulder
Mechanism of Labor: Cardinal Movements
- The mechanism of labor describes the series of position changes a fetus undergoes during passage through the birth canal, focusing on the smallest diameters
- Descent: The widest part (biparietal diameter for cephalic presentation) passes through the pelvic inlet
- Flexion: The fetal head flexes forward for the smallest anteroposterior diameter (suboccipitobregmatic) to present to the birth canal
- Internal Rotation: The fetal head rotates to align the anteroposterior diameter with the anteroposterior plane of the pelvis, bringing the shoulders into the best position for the inlet
- Extension: As the occiput is born, the neck acts as a pivot for the head to extend, with the face and chin being born last
- External Rotation: Immediately after the head is born, it rotates back to the diagonal or transverse position, aligning the shoulders in the anteroposterior position for optimal outlet passage
- Expulsion: The body of the fetus follows the head and shoulders, being born quickly afterwards
Phases of Labor: Uterine Contractions
- Uterine contractions are the primary force for labor, characterized by rhythmicity and progressive intensity
- Each contraction has three phases: increment (increasing intensity), acme (strongest contraction), and decrement (decreasing intensity)
- Effective contractions are necessary for cervical dilation and fetal descent
Cervical Changes: Effacement and Dilation
- Effacement: Shortening and thinning of the cervical canal; normally 1 to 2 cm long
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Description
Explore the physiological factors contributing to the onset of labor and understand the significance of pelvic structure for childbirth. This quiz delves into hormonal influences, uterine stretch responses, and critical pelvic measurements that impact labor progression. Enhance your knowledge of maternal-fetal dynamics and childbirth preparation.
