This is one of the cornerstone chapters of the entire book. If I were designing a midwifery curriculum, Chapters 8 (Placenta), 9 (Embryology), 11 (Physiologic Adaptations), 13 (Physiology of Parturition), and 14 (Labor) would be the core science chapters. Everything else builds on them.
Chapter 13 answers one of the biggest questions in obstetrics:
“Why does labor begin?”
The honest answer, even today, is that we don’t completely know. This chapter explores the leading theories and explains the physiologic changes that prepare the uterus, cervix, fetus, and placenta for birth.
Chapter 13 – Physiology of Parturition
- Read Coad, Anatomy & Physiology for Midwives, 4th edition, chapter 13.
- Write out your answers to Coad, Chapter Case Study, page 372.
- Create a Coad “Chapter 13 Study Sheet.” Include the following:
Learning Goals
□ Describe how the uterus prepares for labor.
□ Explain current theories of labor initiation.
□ Describe the hormonal regulation of labor.
□ Explain methods of induction and augmentation of labor.
□ Describe preterm labor and its causes.
□ Explain the physiologic effects of labor on mother and baby.
□ Describe the physiology of labor pain.
□ Explain the rationale behind methods of pain relief.
Essential Vocabulary
Labor
- Parturition
- Labor
- Uterine contractions
- Braxton Hicks contractions
- Cervical ripening
- Cervical effacement
- Cervical dilation
- Uterine quiescence
- Myometrium
Hormones
- Oxytocin
- Prostaglandins
- Progesterone withdrawal (functional)
- Estrogen
- Cortisol
- CRH (Corticotropin-Releasing Hormone)
- Relaxin
Labor Physiology
- Gap junctions
- Oxytocin receptors
- Ferguson reflex
- Positive feedback
- Fundal dominance
Preterm Labor
- Preterm labor
- PPROM
- Tocolytics
- Corticosteroids
- Cervical insufficiency
Pain
- Visceral pain
- Somatic pain
- Endorphins
- Catecholamines
Draw
1. Theories of Labor Initiation
Baby Matures
↓
Placenta Ages
↓
Hormonal Changes
↓
Prostaglandins ↑
↓
Oxytocin Sensitivity ↑
↓
Labor2. Positive Feedback Loop
This is probably the single most important diagram.
Baby presses on cervix
↓
Stretch receptors
↓
Oxytocin release
↓
Stronger contractions
↓
More cervical pressure
↓
More oxytocinLabel this:
Ferguson Reflex
3. Uterine Contraction
Draw:
Fundus
↓↓↓
Baby
↓
Cervix opens
Illustrate that contractions normally begin at the fundus and move downward (fundal dominance), helping to push the baby toward the cervix.
Concepts I Must Know
| Concept | Importance |
|---|---|
| Uterine quiescence | Keeps pregnancy intact |
| Cervical ripening | Prepares cervix for labor |
| Gap junctions | Coordinate contractions |
| Oxytocin receptors | Increase near labor |
| Ferguson reflex | Positive feedback during labor |
| Functional progesterone withdrawal | One proposed trigger for labor |
| Prostaglandins | Ripen cervix and stimulate contractions |
Processes I Must Understand
- Preparation of the uterus
- Cervical ripening
- Hormonal changes before labor
- Labor initiation theories
- Positive feedback
- Preterm labor
- Induction
- Augmentation
- Maternal physiologic responses
- Fetal physiologic responses
Midwifery Connections
| Concept | Why a Midwife Cares |
|---|---|
| Cervical ripening | Assessing readiness for labor |
| Oxytocin physiology | Understanding normal labor progress |
| Ferguson reflex | Supporting physiologic birth |
| Catecholamines | Stress can inhibit labor |
| Endorphins | Natural pain management |
| Prostaglandins | Natural and medical induction |
| Preterm labor | Recognition and management |
| Uterine efficiency | Evaluating dysfunctional labor |
Clinical Connections
Be able to explain:
- Why labor usually does not begin until fetal maturity.
- Why no single hormone “starts labor.”
- Why contractions become more coordinated as labor approaches.
- Why movement and upright positioning may enhance labor.
- Why excessive maternal fear or stress may slow labor (through elevated catecholamines).
- Why induction is more successful with a favorable cervix.
- Why corticosteroids are given when preterm birth is anticipated (to accelerate fetal lung maturation).
- Why tocolytics delay labor rather than stop it permanently.
Things Worth Memorizing
Hormones
- Oxytocin strengthens contractions.
- Prostaglandins ripen the cervix.
- Estrogen increases uterine sensitivity to oxytocin.
- Functional progesterone withdrawal is thought to contribute to labor onset.
Uterus
Near labor:
- More oxytocin receptors
- More gap junctions
- Better coordinated contractions
Labor
Know the difference between:
- Induction = starting labor.
- Augmentation = strengthening labor that has already begun.
Preterm Labor
Know:
- Risk factors
- Signs
- General management principles
Questions I Should Answer Without Looking
- What is parturition?
- Why doesn’t labor begin at 30 weeks?
- What role does oxytocin play?
- What do prostaglandins do?
- What is cervical ripening?
- What are gap junctions?
- What is the Ferguson reflex?
- Why are contractions a positive feedback system?
- What is the difference between induction and augmentation?
- What causes preterm labor?
Compendium Entry
This chapter deserves six pages because it forms the scientific foundation for understanding normal labor.
Page 1 – Preparing for Labor
- Uterine quiescence
- Cervical ripening
- Hormonal changes
- Myometrial changes
Page 2 – Hormones of Labor
Create a chart:
| Hormone | Primary Role |
|---|---|
| Oxytocin | Strengthens contractions |
| Prostaglandins | Cervical ripening and uterine contractions |
| Estrogen | Increases uterine responsiveness |
| Progesterone | Maintains pregnancy; functional withdrawal contributes to labor |
| CRH | May influence timing of labor |
| Cortisol | Fetal maturation and possible role in labor initiation |
Page 3 – Labor Initiation Theories
Summarize the major theories:
- Fetal signaling
- Placental aging
- Functional progesterone withdrawal
- Estrogen predominance
- Mechanical uterine stretch
- Inflammatory signaling
Include a note that labor likely results from multiple interacting pathways rather than a single trigger.
Page 4 – Positive Feedback
Illustrate:
Cervix → Oxytocin → Contractions → More cervical stretch.
This page should include the Ferguson reflex and explain why labor is one of the classic examples of a positive feedback system in physiology.
Page 5 – Preterm Labor
Include:
- Risk factors
- Signs and symptoms
- PPROM
- Tocolytics
- Antenatal corticosteroids
- Magnesium sulfate for fetal neuroprotection (where indicated)
Page 6 – Physiology of Labor Pain
Organize pain by stage:
| Stage | Source of Pain |
|---|---|
| First stage | Uterine contractions and cervical dilation (visceral pain) |
| Second stage | Stretching of the vagina and perineum (somatic pain) |
| Transition | Combination of both with intense physiologic and emotional responses |
Include factors that may modify pain:
- Endorphins
- Catecholamines
- Fear
- Relaxation
- Continuous labor support
- Position changes
- Water immersion
Quick Reference Cards
This chapter naturally lends itself to these cards:
- Hormones of Labor
- Theories of Labor Initiation
- Ferguson Reflex
- Positive Feedback in Labor
- Gap Junctions
- Cervical Ripening
- Induction vs. Augmentation
- Oxytocin
- Prostaglandins
- Preterm Labor
- PPROM
- Physiology of Labor Pain
- Maternal Physiologic Changes During Labor
- Fetal Adaptations During Labor
One study technique I’d especially recommend
As a future midwife, don’t just memorize what happens—always ask why.
For example:
| Change | Why It Happens |
|---|---|
| Increased oxytocin receptors | Makes the uterus increasingly responsive as term approaches. |
| More gap junctions | Allows uterine muscle cells to contract as a coordinated unit rather than independently. |
| Cervical ripening | Softens and remodels cervical collagen so dilation can occur with less resistance. |
| Prostaglandin production | Promotes cervical softening and enhances uterine contractility. |
| Endorphin release | Provides natural analgesia, helping the mother cope with labor. |
| Fetal cortisol increases | Contributes to fetal organ maturation and may participate in signaling that birth is approaching. |
This chapter also pairs beautifully with childbirth education. As you teach about movement, upright positioning, relaxation, water immersion, or reducing fear in labor, you’ll be able to connect each recommendation back to the underlying physiology rather than presenting it as merely a technique. That physiological understanding is what distinguishes a midwife from someone who has simply memorized birth practices.
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