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Questions and Answers
What is the primary purpose of dilatation of the cervical os during labor?
What is the primary purpose of dilatation of the cervical os during labor?
What occurs during the formation of the bag of waters?
What occurs during the formation of the bag of waters?
What is indicated if the membranes rupture before signs of true labor?
What is indicated if the membranes rupture before signs of true labor?
What contributes to general fluid pressure during contractions?
What contributes to general fluid pressure during contractions?
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What causes the bleeding associated with the cervical plug during labor?
What causes the bleeding associated with the cervical plug during labor?
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Which factor affects the progress of labor by influencing the shape of the fetal head?
Which factor affects the progress of labor by influencing the shape of the fetal head?
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What is the term for the relationship between the fetal body parts?
What is the term for the relationship between the fetal body parts?
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At what age does the anterior fontanelle typically close?
At what age does the anterior fontanelle typically close?
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Which of the following is NOT considered one of the bones that make up the fetal head?
Which of the following is NOT considered one of the bones that make up the fetal head?
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What is assessed to determine the degree of engagement during labor?
What is assessed to determine the degree of engagement during labor?
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Which of the following sutures is located between the occipital and parietal bones?
Which of the following sutures is located between the occipital and parietal bones?
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During which stage does the fetal engagement occur in multipara compared to primipara?
During which stage does the fetal engagement occur in multipara compared to primipara?
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What is the significance of the anterior fontanelle in relation to fetal skull development?
What is the significance of the anterior fontanelle in relation to fetal skull development?
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What is the cervical dilatation range in the latent phase of the first stage of labor?
What is the cervical dilatation range in the latent phase of the first stage of labor?
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During which phase is the maternal behavior likely to be described as irritable and uncooperative?
During which phase is the maternal behavior likely to be described as irritable and uncooperative?
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What is the typical duration of uterine contractions during the transitional phase?
What is the typical duration of uterine contractions during the transitional phase?
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At what point in the labor process should the membrane have ruptured?
At what point in the labor process should the membrane have ruptured?
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In which stage do uterine contractions occur every 2 to 3 minutes according to the content?
In which stage do uterine contractions occur every 2 to 3 minutes according to the content?
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What is the site of pain commonly experienced during true labor?
What is the site of pain commonly experienced during true labor?
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What does a woman typically experience as a sign during the second stage of labor?
What does a woman typically experience as a sign during the second stage of labor?
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How do true and false labor pains differ in terms of cervical dilatation?
How do true and false labor pains differ in terms of cervical dilatation?
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During which labor phase does a mother generally feel talkative and excited?
During which labor phase does a mother generally feel talkative and excited?
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What happens to the uterine contractions during the acme phase?
What happens to the uterine contractions during the acme phase?
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What is the expected frequency of contractions in the active phase?
What is the expected frequency of contractions in the active phase?
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What is the primary hormonal change that occurs shortly before the onset of labor?
What is the primary hormonal change that occurs shortly before the onset of labor?
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What is the term used to describe the period of time between the beginning of one contraction to the beginning of the next?
What is the term used to describe the period of time between the beginning of one contraction to the beginning of the next?
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Which theory suggests that uterine contractions are stimulated by the mechanical pressure of a growing fetus?
Which theory suggests that uterine contractions are stimulated by the mechanical pressure of a growing fetus?
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What role do prostaglandins play in the labor process?
What role do prostaglandins play in the labor process?
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Which of the following is a key role of uterine contractions during labor?
Which of the following is a key role of uterine contractions during labor?
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What characterizes the bulging of membranes during true labor?
What characterizes the bulging of membranes during true labor?
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What is the effect of oxytocin during labor?
What is the effect of oxytocin during labor?
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Which factor does NOT affect the progress of labor?
Which factor does NOT affect the progress of labor?
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How does sedative relief differ between true and false labor?
How does sedative relief differ between true and false labor?
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What is the intensity range of uterine contractions during the acme phase?
What is the intensity range of uterine contractions during the acme phase?
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How does the placental ischemic theory contribute to the onset of labor?
How does the placental ischemic theory contribute to the onset of labor?
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What aspect of the '5Ps' does 'Power' refer to in labor?
What aspect of the '5Ps' does 'Power' refer to in labor?
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What effect does a sudden decrease in progesterone before labor have on the uterus?
What effect does a sudden decrease in progesterone before labor have on the uterus?
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What occurs during the second stage of labor when the presenting part descends?
What occurs during the second stage of labor when the presenting part descends?
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Which of the following describes the flexion of the fetal head during labor?
Which of the following describes the flexion of the fetal head during labor?
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How is the degree of descent of the presenting part evaluated?
How is the degree of descent of the presenting part evaluated?
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What is NOT a sign associated with the second stage of labor?
What is NOT a sign associated with the second stage of labor?
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Which factor contributes to the descent of the presenting part during labor?
Which factor contributes to the descent of the presenting part during labor?
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What happens to the anal orifice during the second stage of labor?
What happens to the anal orifice during the second stage of labor?
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What is the presenting diameter achieved during flexion?
What is the presenting diameter achieved during flexion?
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During internal rotation of the fetal head, how many degrees does the head rotate?
During internal rotation of the fetal head, how many degrees does the head rotate?
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Study Notes
Introduction to Physiology of Normal Labor
- The physiology of normal labor encompasses the process of uterine contractions, cervical changes, and ultimately, the delivery of a viable fetus and placenta.
- Normal labor is defined as a complete and spontaneous process of delivering a full-term, single, viable fetus, presenting by vertex, within 24 hours of the onset of true labor pains through the natural birth canal, without assistance, and without complications to the mother or the newborn.
- Duration of normal labor varies between women, with primiparas lasting typically 12-18 hours and multiparas lasting around 6-10 hours.
- Prolonged labor lasts more that 24 hours.
- Precipitate labor lasts less than 3 hours.
- Premature labor results in delivery of a premature fetus and occurs at a gestational age between 28-37 weeks.
Theories of Labor Onset
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The exact cause of labor onset is unknown, but several theoretical explanations exist.
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Progesterone Withdrawal Theory: Progesterone suppresses uterine irritability throughout pregnancy, counterbalancing estrogen's increased uterine contractility. A sudden decrease in progesterone levels, combined with increased estrogen, triggers oxytocin receptor upregulation. Increased oxytocin receptors lead to expulsive uterine contractions.
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Prostaglandin Production Theory: Progesterone withdrawal also activates prostaglandins, which stimulate smooth muscle contraction in the myometrium and cervix. Prostaglandins promote cervical ripening and encourage uterine contractions.
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Uterine Distention Theory (Mechanical): As the fetus grows, the increasing intra-abdominal pressure eventually initiates labor.
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Placental Ischemic Theory: Decreased blood flow to the placenta during later stages of pregnancy results in ischemia and the secretion of oxytocin, triggering labor.
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Oxytocin Stimulation Theory: Oxytocin levels slowly increase throughout pregnancy, increasing during labor and peaking in the second stage. Oxytocin enhances myometrial contractions and increases myometrium sensitivity to prostaglandins.
Factors Affecting Labor Progress (5Ps)
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Passenger: The fetus (size, presentation, position), placenta, membranes, umbilical cord, and amniotic fluid. Crucial factors include fetal head size and molding, attitude, lie and presentation.
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Passage: The birth canal and bony pelvis, including diameter, shape, and alignment.
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Power: Uterine contractions, including frequency, intensity, and duration, as well as bearing-down efforts.
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Position: Maternal position during labor and birth.
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Psyche: Maternal psychological response to labor.
Signs of Premonitory Labor Symptoms
- Lightening: The fetus descends into the true pelvis.
- Frequency of urination: Increased urinary frequency due to pressure on the bladder.
- Cervical Effacement: Shortening or thinning of the cervix.
- Braxton Hicks contractions: Irregular uterine contractions.
- Cervical Ripening: Softening of the cervix..
Signs of True Labor
- Bloody Show: expulsion of mucus plug streaked with blood (due to ruptured small vessels).
- Cervical Dilation: Dilation of the cervical os.
- Formation of the bag of waters during contractions: Rupture of membranes (amniotic fluid leakage).
- Uterine Contractions: Increasing frequency, duration, and intensity.
Nature of Uterine Contractions
- Uterine contractions have three phases: increment (pressure increases), acme (maximal or peak pressure), and decrement (pressure decreases).
- Pain is typically experienced when the intrauterine pressure reaches 20-25 mmHg.
- Uterine muscle maintains some shorting after contraction (retraction).
Stages of Labor
- First Stage: Cervical dilation and effacement. Divided into latent, active, and transitional phases.
- Second Stage: Expulsion of the fetus.
- Third Stage: Expulsion of the placenta. Can involve the use of controlled cord traction.
- Fourth Stage: Postpartum recovery.
Mechanisms of Placental Separation
- Schultze's Mechanism (80%): Central placental separation, presenting the fetal surface first.
- Duncan's Mechanism (20%): Lower pole separation, presenting the maternal surface first.
Placenta Variations
- Battledore Insertion: Placental insertion at the edge.
- Circummarginal Insertion: Placental insertion at the periphery.
- Velamentous Insertion: Placental vessels detaching from the chorion.
- Bipartite (Bilobed) Placenta: Two distinct placental lobes.
- Succenturiate Lobe: Accessory placental lobe.
- Circumvallate Placenta: A ring of tissue surrounds the placental margin.
Fourth Stage of Labor
- The fourth stage of labor is the period immediately following the delivery of the placenta. It is a critical time for observation and ensure uterus contractions lead to a stable uterus, prevents uterine inversion and bleeding.
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Description
This quiz covers the key physiological aspects of normal labor, including uterine contractions, cervical changes, and the delivery process. It also discusses the duration of labor and various types of labor such as prolonged and precipitate labor. Explore the theories behind labor onset and the definitions associated with normal birth.
