Introduction to Physiology of Normal Labor
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Questions and Answers

What is the primary purpose of dilatation of the cervical os during labor?

  • To allow the baby to stay in utero longer
  • To permit the passage of the fetus (correct)
  • To minimize uterine contractions
  • To prepare the cervix for hormone release

What occurs during the formation of the bag of waters?

  • The amniotic fluid is completely absorbed
  • The cervical os remains tightly closed
  • The lower part of the membrane bulges through the dilating cervix (correct)
  • The cervical plug is fully retained

What is indicated if the membranes rupture before signs of true labor?

  • It may indicate a prolapsed cord (correct)
  • The labor will be delayed
  • It guarantees the baby's arrival within minutes
  • Labor is likely to be normal and uncomplicated

What contributes to general fluid pressure during contractions?

<p>The intact membranes exerting pressure on the fluid (B)</p> Signup and view all the answers

What causes the bleeding associated with the cervical plug during labor?

<p>Rupture of minute capillaries during separation (A)</p> Signup and view all the answers

Which factor affects the progress of labor by influencing the shape of the fetal head?

<p>Molding (C)</p> Signup and view all the answers

What is the term for the relationship between the fetal body parts?

<p>Fetal lie (C)</p> Signup and view all the answers

At what age does the anterior fontanelle typically close?

<p>12-18 months (A)</p> Signup and view all the answers

Which of the following is NOT considered one of the bones that make up the fetal head?

<p>Sphenoid bone (A)</p> Signup and view all the answers

What is assessed to determine the degree of engagement during labor?

<p>Vaginal and cervical examination (C)</p> Signup and view all the answers

Which of the following sutures is located between the occipital and parietal bones?

<p>Lambdoid suture (B)</p> Signup and view all the answers

During which stage does the fetal engagement occur in multipara compared to primipara?

<p>Before labor for primipara and during for multipara (A)</p> Signup and view all the answers

What is the significance of the anterior fontanelle in relation to fetal skull development?

<p>It allows for the skull's molding during birth. (A)</p> Signup and view all the answers

What is the cervical dilatation range in the latent phase of the first stage of labor?

<p>1-3 cm (B)</p> Signup and view all the answers

During which phase is the maternal behavior likely to be described as irritable and uncooperative?

<p>Transitional Phase (C)</p> Signup and view all the answers

What is the typical duration of uterine contractions during the transitional phase?

<p>60-90 seconds (B)</p> Signup and view all the answers

At what point in the labor process should the membrane have ruptured?

<p>By the end of the First Stage (C)</p> Signup and view all the answers

In which stage do uterine contractions occur every 2 to 3 minutes according to the content?

<p>Second Stage (C)</p> Signup and view all the answers

What is the site of pain commonly experienced during true labor?

<p>Abdomen and lower back (A)</p> Signup and view all the answers

What does a woman typically experience as a sign during the second stage of labor?

<p>Involuntary bearing down (C)</p> Signup and view all the answers

How do true and false labor pains differ in terms of cervical dilatation?

<p>True labor causes progressive dilatation (A)</p> Signup and view all the answers

During which labor phase does a mother generally feel talkative and excited?

<p>Latent Phase (C)</p> Signup and view all the answers

What happens to the uterine contractions during the acme phase?

<p>Intra-uterine pressure reaches its maximum (B)</p> Signup and view all the answers

What is the expected frequency of contractions in the active phase?

<p>3/10 to 4/10 minutes (A)</p> Signup and view all the answers

What is the primary hormonal change that occurs shortly before the onset of labor?

<p>Decrease in progesterone (A)</p> Signup and view all the answers

What is the term used to describe the period of time between the beginning of one contraction to the beginning of the next?

<p>Frequency (A)</p> Signup and view all the answers

Which theory suggests that uterine contractions are stimulated by the mechanical pressure of a growing fetus?

<p>Uterine distention theory (C)</p> Signup and view all the answers

What role do prostaglandins play in the labor process?

<p>They promote cervical thinning and stimulates uterine contractions. (B)</p> Signup and view all the answers

Which of the following is a key role of uterine contractions during labor?

<p>To promote cervical effacement and dilation (C)</p> Signup and view all the answers

What characterizes the bulging of membranes during true labor?

<p>It is present (C)</p> Signup and view all the answers

What is the effect of oxytocin during labor?

<p>It stimulates myometrial contractions and increases prostaglandin release. (D)</p> Signup and view all the answers

Which factor does NOT affect the progress of labor?

<p>Placental location (A)</p> Signup and view all the answers

How does sedative relief differ between true and false labor?

<p>False labor is relieved by sedatives (B)</p> Signup and view all the answers

What is the intensity range of uterine contractions during the acme phase?

<p>30-55 mmHg (A)</p> Signup and view all the answers

How does the placental ischemic theory contribute to the onset of labor?

<p>It causes degeneration of the placenta, leading to oxytocin secretion. (C)</p> Signup and view all the answers

What aspect of the '5Ps' does 'Power' refer to in labor?

<p>The strength of uterine contractions (D)</p> Signup and view all the answers

What effect does a sudden decrease in progesterone before labor have on the uterus?

<p>It increases uterine irritability and contractions. (D)</p> Signup and view all the answers

What occurs during the second stage of labor when the presenting part descends?

<p>Increase in the frequency, duration, and intensity of uterine contractions (D)</p> Signup and view all the answers

Which of the following describes the flexion of the fetal head during labor?

<p>The chin comes in contact with the fetal thorax (B)</p> Signup and view all the answers

How is the degree of descent of the presenting part evaluated?

<p>By assessing the station of the presenting part (B)</p> Signup and view all the answers

What is NOT a sign associated with the second stage of labor?

<p>Cessation of contractions (B)</p> Signup and view all the answers

Which factor contributes to the descent of the presenting part during labor?

<p>Pressure of the amniotic fluid (C)</p> Signup and view all the answers

What happens to the anal orifice during the second stage of labor?

<p>The anal orifice starts to dilate (A)</p> Signup and view all the answers

What is the presenting diameter achieved during flexion?

<p>Suboccipitobregmatic diameter (C)</p> Signup and view all the answers

During internal rotation of the fetal head, how many degrees does the head rotate?

<p>45 degrees anteriorly (B)</p> Signup and view all the answers

Flashcards

Premature labor definition

Labor occurring between 28 and 37 weeks of gestation, resulting in a premature fetus.

Progesterone's role in pregnancy

Progesterone counteracts estrogen's effect on uterine contractions, keeping the uterus calm during pregnancy.

Estrogen's role in labor

Estrogen increases in late pregnancy, raising oxytocin receptors in the uterus and resulting in more contractions.

Prostaglandins and labor onset

Prostaglandins, stimulated by progesterone withdrawal, soften the cervix and strengthen uterine contractions, initiating labor.

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Uterine distention theory

Increased fetal size and pressure in the uterus, causing labor to begin.

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Placental ischemia in labor

Reduced blood flow to the placenta, potentially causing labor by releasing oxytocin-like substances.

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Oxytocin's double action in labor

Oxytocin causes myometrial contractions and stimulates prostaglandin release, increasing uterine sensitivity.

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Factors affecting labor (5Ps):

Passenger (baby), Passage (birth canal), Powers (uterine contractions), Position (mother), and Psyche (mother's mental state).

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Fetal Head Sutures

Fibrous bands connecting fetal skull bones

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Fetal Head Fontanelles

Junction points of sutures; soft spots on the fetal skull

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Anterior Fontanelle

Large, diamond-shaped soft spot on fetal skull (between frontal and parietal bones)

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Posterior Fontanelle

Small, triangular soft spot, closes earlier (between occipital and parietal bones)

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Fetal Head Molding

Overlapping of fetal head bones to decrease size for easier delivery

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Engagement

Fetal presenting part settling into the pelvis (at the level of ischial spines)

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Primipara's Engagement

Engagement of the fetal head occurs 10-14 days before labor

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Multipara's Engagement

Engagement of the fetal part occurs during labor for a woman who has had more than one baby

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Formation of the bag of waters

During labor, as the cervix dilates, the lower part of the amniotic sac detaches and bulges through the cervix. This creates fore water (fluid trickling out) and hind water (remaining fluid).

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Rupture of membranes

The breaking of the amniotic sac, which may occur before true labor begins (premature rupture of membranes) or during labor. It can signal a risk of prolapsed cord if the baby's head isn't engaged (settled in the pelvis).

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True labor pains

Uterine contractions that become more frequent, stronger, and longer over time.

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Cervical dilation

The opening of the cervix (the neck of the uterus) to 10 centimeters, allowing the baby to pass through.

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Show

The cervical plug, which is a mucus plug that seals the cervix during pregnancy. It may be discharged during labor, often tinged with blood due to ruptured capillaries.

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False Labor Pains (Braxton Hicks)

Irregular contractions that do not cause cervical dilation and can be relieved by sedatives.

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What are the three phases of a uterine contraction?

Increment: The intra-uterine pressure begins to increase. Acme: The pressure reaches its peak. Decrement: The intra-uterine pressure decreases or fades.

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Frequency of Uterine Contractions

The time between the beginning of one contraction and the beginning of the next.

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Duration of Uterine Contractions

The time from the start of the increment to the end of the decrement.

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Intensity of Uterine Contraction

The strength of the contraction during its peak (acme).

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What does a uterine contraction do?

Contractions help efface and dilate the cervix, engage and rotate the fetus, separate and expel the placenta, and restore normal muscle tone to the uterus.

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What happens when intra-uterine pressure is around 20-25mmHg?

Pain is experienced.

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Cervical Effacement

The thinning of the cervix, measured as a percentage from 0% (thick) to 100% (fully thinned).

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Uterine Contraction Frequency

How often uterine contractions happen, measured as contractions per 10 minutes.

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Uterine Contraction Duration

How long each uterine contraction lasts, measured in seconds.

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Uterine Contraction Intensity

The strength of uterine contractions, usually described as mild, moderate, or strong.

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Involuntary Bearing Down

The uncontrollable urge to push during the second stage of labor.

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Rupture of the Bag of Water

The breaking of the amniotic sac (water bag) during labor, releasing amniotic fluid.

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Bearing Down

The intentional pushing effort during the second stage of labor to help deliver the baby.

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Pelvic Floor Displacement

During labor, the bladder is pulled upwards into the abdomen, creating more space in the pelvis for the baby to pass through. This causes a feeling of pressure on the rectum and the urge to defecate.

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Anal Gaping

As the baby descends, the anus expands to a diameter of 2.5 cm, making it seem like it is opening up.

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Leg Cramps in Labor

The baby's head pressing against the sacral nerve can cause leg cramps, a common discomfort during labor.

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Presenting Part Recoil

During contractions, the baby's head appears at the vaginal opening, but then disappears between contractions.

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Perineal Bulging

The perineum (the area between the vagina and anus) stretches and bulges out as the baby descends.

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Descent During Labor

The progress of the baby's presenting part (usually the head) through the pelvis.

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Flexion of Fetal Head

The baby's head flexes as it meets resistance from the pelvis, bringing the chin to the chest. This changes the presenting diameter to the smallest possible.

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Internal Rotation of Fetal Head

The baby's head rotates 45 degrees to align itself with the birth canal.

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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

  • The exact cause of labor onset is unknown, but several theoretical explanations exist.

  • 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.

  • 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.

  • Uterine Distention Theory (Mechanical): As the fetus grows, the increasing intra-abdominal pressure eventually initiates labor.

  • Placental Ischemic Theory: Decreased blood flow to the placenta during later stages of pregnancy results in ischemia and the secretion of oxytocin, triggering labor.

  • 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)

  • 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.

  • Passage: The birth canal and bony pelvis, including diameter, shape, and alignment.

  • Power: Uterine contractions, including frequency, intensity, and duration, as well as bearing-down efforts.

  • Position: Maternal position during labor and birth.

  • 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.

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