This chapter is where all the previous chapters begin to come together. Chapters 1–10 explained the building blocks of pregnancy: physiology, hormones, fertilization, embryology, the placenta, and immunity. Chapter 11 asks, “How does the mother’s body adapt to support all of that?”
For a practicing midwife, this is one of the most clinically useful chapters. Nearly every common discomfort of pregnancy—and many normal lab value changes—can be explained by the physiologic adaptations discussed here.
Chapter 11 – Physiological Adaptation to Pregnancy
- Read Coad, Anatomy & Physiology for Midwives, 4th edition, chapter 11.
- Write out your answers to Coad, Chapter Case Study, page 296.
- Create a Coad “Chapter 11 Study Sheet.” Include the following:
Learning Goals
□ Explain the hormonal changes that drive maternal adaptations.
□ Describe cardiovascular adaptations during pregnancy.
□ Describe respiratory adaptations during pregnancy.
□ Describe gastrointestinal adaptations during pregnancy.
□ Explain changes in carbohydrate metabolism.
□ Explain iron requirements during pregnancy.
□ Relate physiologic adaptations to normal pregnancy symptoms and discomforts.
Essential Vocabulary
Hormones
- hCG
- Progesterone
- Estrogen
- Human placental lactogen (hPL)
- Relaxin
- Oxytocin
- Prolactin
Cardiovascular
- Cardiac output
- Blood volume
- Stroke volume
- Heart rate
- Systemic vascular resistance
- Hemodilution
- Physiologic anemia
Respiratory
- Tidal volume
- Minute ventilation
- Oxygen consumption
- Diaphragm elevation
- Dyspnea
Gastrointestinal
- Gastric emptying
- Gastroesophageal reflux
- Constipation
- Hemorrhoids
- Gallbladder stasis
Renal
- Glomerular filtration rate (GFR)
- Hydronephrosis
- Urinary frequency
Metabolic
- Insulin resistance
- Glucose metabolism
- Iron deficiency
- Basal metabolic rate
Draw
1. Maternal Adaptations by System
Pregnancy
↓
Hormones
↓
Cardiovascular
Respiratory
Renal
GI
Endocrine
Musculoskeletal
Skin2. Blood Volume Changes
Draw a graph showing:
- Plasma volume ↑↑
- Red blood cells ↑
- Hemoglobin concentration ↓ (physiologic dilution)
3. Cardiac Output
Simple diagram:
Cardiac Output
=
Heart Rate ↑
Stroke Volume ↑
4. Oxygen Supply
Mother
↓
Lungs
↓
Placenta
↓
Baby
Illustrate why maternal oxygen needs increase.
Systems I Must Know
| System | Major Pregnancy Changes |
|---|---|
| Cardiovascular | ↑ blood volume, ↑ cardiac output, ↓ vascular resistance |
| Respiratory | ↑ tidal volume, mild hyperventilation |
| Renal | ↑ GFR, urinary frequency |
| GI | Slower motility, reflux, constipation |
| Endocrine | Placental hormones dominate |
| Metabolic | ↑ insulin resistance, ↑ energy needs |
| Hematologic | Physiologic anemia, hypercoagulability |
Processes I Must Understand
- Hormonal adaptation
- Plasma volume expansion
- Increased cardiac output
- Maternal respiratory compensation
- Renal adaptation
- Glucose metabolism
- Iron metabolism
- Preparation for labor and breastfeeding
Midwifery Connections
| Concept | Why a Midwife Cares |
|---|---|
| Increased blood volume | Helps tolerate blood loss at birth |
| Hypercoagulability | Increases clotting risk postpartum |
| Physiologic anemia | Distinguishes normal from pathologic anemia |
| Increased GFR | Affects urine testing and medication dosing |
| Relaxin | Pelvic discomfort and ligament laxity |
| hPL | Gestational diabetes risk |
| Progesterone | Explains reflux, constipation, urinary stasis |
| Increased oxygen demand | Explains mild shortness of breath |
Clinical Connections
Be able to explain:
- Why pregnant women become short of breath even with healthy lungs.
- Why blood pressure often falls slightly in mid-pregnancy.
- Why heart rate increases during pregnancy.
- Why physiologic anemia develops.
- Why iron requirements increase.
- Why reflux and constipation are common.
- Why urinary frequency occurs in both early and late pregnancy.
- Why insulin resistance increases during pregnancy.
- Why edema may be normal yet still requires assessment.
Things Worth Memorizing
Cardiovascular
- Blood volume increases significantly.
- Cardiac output increases.
- Heart rate increases modestly.
- Systemic vascular resistance decreases.
Respiratory
- Oxygen consumption increases.
- Tidal volume increases.
- Minute ventilation increases.
Renal
- GFR increases.
- Urinary frequency is common.
GI
- Progesterone slows smooth muscle.
- Constipation becomes more common.
- Reflux becomes more common.
Endocrine
Know the major placental hormones and their primary effects.
Questions I Should Answer Without Looking
- Why does blood volume increase during pregnancy?
- Why is physiologic anemia considered normal?
- Why does cardiac output increase?
- Why does progesterone contribute to constipation?
- Why do pregnant women experience reflux?
- Why does insulin resistance increase?
- Why does iron demand increase?
- Why is mild shortness of breath common?
- Why is urinary frequency expected?
- Which changes prepare the mother for labor and breastfeeding?
Compendium Entry
This chapter deserves six pages in your Midwifery Compendium because it becomes a reference for many later topics.
Page 1 – Hormonal Adaptations
- hCG
- Estrogen
- Progesterone
- hPL
- Relaxin
- Prolactin
- Oxytocin
Page 2 – Cardiovascular Changes
- Blood volume
- Cardiac output
- Heart rate
- Blood pressure
- Physiologic anemia
Page 3 – Respiratory & Renal Changes
- Oxygen needs
- Ventilation
- GFR
- Urinary tract changes
Page 4 – Gastrointestinal & Metabolic Changes
- Reflux
- Constipation
- Gallbladder
- Glucose metabolism
- Iron
Page 5 – Common Pregnancy Symptoms Explained
Instead of memorizing symptoms separately, organize them by physiologic cause.
| Symptom | Physiologic Explanation |
|---|---|
| Nausea | Hormonal changes (especially early pregnancy) |
| Fatigue | Increased metabolic demand and hormonal shifts |
| Frequent urination | Increased GFR and uterine pressure |
| Reflux | Progesterone relaxes the lower esophageal sphincter; enlarging uterus increases pressure |
| Constipation | Slowed intestinal motility from progesterone |
| Shortness of breath | Increased oxygen demand and diaphragm elevation |
| Mild edema | Increased plasma volume and venous compression |
| Dizziness | Vasodilation and changes in blood pressure |
| Leg cramps | Multifactorial—circulatory and musculoskeletal changes |
| Back pain | Shift in center of gravity and ligament laxity |
Page 6 – Normal vs. Concerning Findings
This is a page you’ll likely consult often.
| Usually Normal | Needs Further Evaluation |
|---|---|
| Mild physiologic anemia | Severe anemia or symptoms out of proportion |
| Mild ankle swelling late in pregnancy | Sudden swelling of face or hands, especially with hypertension |
| Mild shortness of breath | Chest pain, severe dyspnea, low oxygen saturation |
| Occasional Braxton Hicks contractions | Regular painful contractions before term |
| Frequent urination | Dysuria, fever, flank pain suggesting UTI |
| Mild reflux | Persistent vomiting with dehydration or weight loss |
Quick Reference Cards
This chapter naturally becomes a rich source for quick-reference cards:
- Physiologic Changes in Pregnancy (Overview)
- Cardiovascular Changes
- Respiratory Changes
- Renal Changes
- Gastrointestinal Changes
- Endocrine Changes
- Hematologic Changes
- Metabolic Changes
- Normal Pregnancy Discomforts
- Physiologic Anemia
- Gestational Iron Requirements
- Normal Vital Sign Changes in Pregnancy
One study technique I’d especially recommend
Rather than memorizing a list of body-system changes, ask a single question whenever you learn a new adaptation:
“How does this help the mother support the baby or prepare for birth?”
For example:
| Adaptation | Purpose |
|---|---|
| Blood volume increases | Provides more blood flow to the uterus and creates a reserve for blood loss at birth. |
| Cardiac output increases | Delivers more oxygen and nutrients to the placenta and maternal tissues. |
| Increased GFR | Removes maternal and fetal waste products more efficiently. |
| Relaxin softens ligaments | Helps prepare the pelvis for birth, though it may contribute to pelvic discomfort. |
| Increased insulin resistance | Makes more glucose available to the growing fetus. |
| Progesterone slows intestinal motility | May improve nutrient absorption, even though it contributes to constipation. |
Viewing the changes as purposeful adaptations rather than isolated facts makes them much easier to remember and provides a framework for explaining normal pregnancy symptoms to your clients. This systems-based approach will also help you distinguish expected physiologic changes from signs that warrant further evaluation.
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