Physiological changes during pregnancy from dc dutta textbook and at the end make a detailed summary chart to download for ready visual memory
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Physiological Changes During Pregnancy
Sourced from Morgan & Mikhail's Clinical Anesthesiology, Creasy & Resnik's Maternal-Fetal Medicine, and Sabiston's Surgery - representing the same standard content covered in DC Dutta's Textbook of Obstetrics.
1. CARDIOVASCULAR SYSTEM
| Parameter | Change | Notes |
|---|---|---|
| Blood volume | +35% | Plasma +55%, RBC mass +45% |
| Cardiac output | +40% at term | Heart rate +20% + Stroke volume +30% |
| Heart rate | +20 bpm | Progressive from 1st trimester |
| Stroke volume | +30% | Due to increased preload |
| Systolic BP | -5% | Nadirs at mid-2nd trimester |
| Diastolic BP | -15% | More dramatic fall |
| Peripheral vascular resistance | -15 to -20% | Progesterone-mediated smooth muscle relaxation |
| Pulmonary resistance | -30% | Prevents pulmonary hypertension |
Key clinical points:
- Plasma volume increase exceeds RBC increase → physiological dilutional anaemia (Hb stays >11 g/dL)
- At term: total blood volume +1000-1500 mL; total ~90 mL/kg
- Aortocaval compression after 20 weeks in supine - 5-10% develop supine hypotension syndrome - always place in left lateral decubitus
- ECG: left axis deviation, T-wave changes, flow murmur (grade I-II systolic)
- Uterine blood flow: 50 mL/min → 500-700 mL/min at term (~10% of CO)
2. RESPIRATORY SYSTEM
| Parameter | Change | Value at Term |
|---|---|---|
| Minute ventilation | +50% | ~12 L/min |
| Tidal volume | +40% | Main driver of ventilation increase |
| Respiratory rate | +15% | Minor contributor |
| O2 consumption | +20-50% | Fetal + placental + maternal demand |
| FRC | -20% | Diaphragm elevated 4 cm |
| Airway resistance | -35% | Progesterone bronchodilation |
| PaCO2 | -15% | 27-32 mmHg (vs 40 normal) |
| PaO2 | +10% | 104-108 mmHg |
| HCO3 | -15% | 18-21 mEq/L (renal compensation) |
| pH | ~7.44 | Compensated respiratory alkalosis |
| P50 (Hb-O2 curve) | +3 mmHg | 27 → 30 mmHg (right shift, +2,3-DPG) |
Clinical pearls:
- Rapid desaturation during apnea: ↓FRC + ↑O2 consumption - pre-oxygenation is mandatory before intubation
- Mucosal edema + capillary engorgement → use smaller ET tube (6.0-6.5 mm), Mallampati worsens near term
- ↓PaCO2 increases CO2 gradient from fetus to mother, facilitating fetal CO2 transfer
3. HEMATOLOGICAL CHANGES
Red cells: Dilutional anaemia (WHO definition: Hb <11 g/dL = anaemia in pregnancy). Hematocrit falls to ~33-34%.
Coagulation - Hypercoagulable state:
- Fibrinogen ↑ 50-250% (most dramatic)
- Factors VII, VIII, IX, X, XII ↑ 30-250%
- Factor XI may decrease; Protein S decreases
- Acquired resistance to activated Protein C
- Net: VTE risk ×5-10 compared to non-pregnant
White cells: Leukocytosis normal - WBC up to 21,000/μL (mainly neutrophilia). Don't use WBC alone to diagnose infection.
Platelets: ↓ 10% (gestational thrombocytopenia); >80,000 safe for regional anaesthesia.
4. RENAL SYSTEM
| Parameter | Change |
|---|---|
| Renal plasma flow | ↑ 50-80% (peaks 2nd trimester) |
| GFR | ↑ 50% (110-150 mL/min) |
| Serum Creatinine | ↓ to ~0.4-0.5 mg/dL |
| Blood Urea Nitrogen | ↓ to ~9 mg/dL |
| Uric acid | ↓ early; rises near term |
| Aldosterone | ↑ 6× |
| Proteinuria | Up to 300 mg/24h = normal |
Other renal changes: Glycosuria with normal blood glucose (↑ GFR exceeds tubular reabsorption); physiological hydronephrosis (right > left due to dextrorotation of uterus); ↑ UTI risk due to stasis + glycosuria.
5. ENDOCRINE SYSTEM
| Gland | Key Change |
|---|---|
| Pituitary | Size ↑ 120% at delivery; Prolactin ↑ 10×; ACTH ↑ 2-4× |
| Adrenal cortex | Total cortisol ↑ 3× (CBG triples); Urinary free cortisol ↑ 2-3×; Aldosterone ↑ 6× |
| Thyroid | TBG ↑ → total T3/T4 ↑; Free T3/T4 and TSH = NORMAL; TSH ↓ slightly in 1st trimester (HCG cross-reactivity) |
| Pancreas | Insulin secretion ↑ (beta cell hyperplasia); hPL causes insulin resistance; Gestational diabetes risk |
6. GASTROINTESTINAL / HEPATIC
- Stomach: LES tone ↓ + gastric motility ↓ → GERD in 60-80%; aspiration risk ↑
- Colon: Constipation (↑ Na+/H2O absorption, ↓ motility, uterine compression); hemorrhoids (dilated portal collaterals)
- Gallbladder: Volume ↑ 2× in 2nd/3rd trimester; emptying slowed; cholesterol gallstones in ~4%
- Liver: Function unchanged; albumin ↓ (dilutional); ALP ↑ (placental); spider nevi + palmar erythema (estrogen); pseudocholinesterase ↓ 25-30%
7. NEUROLOGICAL / ANAESTHESIA
- MAC ↓ 40% for all volatile anaesthetics (progesterone-mediated); normalizes by day 3 postpartum
- Local anaesthetic sensitivity ↑ - epidural/spinal dose requirements ↓ up to 30%
- Epidural venous plexus engorged → ↑ cephalad spread, ↑ intravascular injection risk, positive epidural pressure
- β-endorphin surge in labor contributes to analgesia
8. METABOLIC
- State resembles accelerated starvation: ↓ fasting glucose, ↑ FFAs, ↑ ketones, ↑ triglycerides
- hPL (human placental lactogen) = key insulin antagonist → diabetogenic state
- Serum calcium ↓ (dilution) but ionized Ca²+ = normal
- Thyroid hormone: total T3/T4 ↑, free fractions normal
- Weight gain: ~11-15 kg total recommended
9. MUSCULOSKELETAL / SKIN / UTERUS
MSK: Relaxin → ligament laxity, pubic symphysis diastasis (1-2 cm), lumbar lordosis ↑, backache very common
Skin: Linea nigra, chloasma (melasma), striae gravidarum, spider nevi, palmar erythema
Uterus: Weight 60 g → 1000 g; capacity 10 mL → 5-10 L; blood flow ×10
Download the Visual Summary Chart
Physiological Changes Pregnancy
Presentation · PPTX
The PPTX contains 9 slides with a color-coded system-by-system layout:
- Title slide with all 9 systems listed
- At-a-glance numerical changes table (all key values at a glance)
- Cardiovascular (6 detailed boxes)
- Respiratory (full table with values + clinical notes)
- Hematological (coagulation, RBC, WBC, platelets)
- Renal + Endocrine (split slide)
- GI / Hepatic / Metabolic (6 boxes)
- Neurological / MSK / Skin / Uterus (6 boxes)
- Master Summary Chart - all 9 systems on one slide for rapid visual revision
Each slide uses a distinct color per system so you can identify the topic at a glance during rapid review.
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