Maternal Physiological Changes

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Maternal Physiological Changes - Heart's Big Load

  • Cardiac Output (CO):30-50%; peaks 20-24 wks.
    • Early: ↑ Stroke Volume (SV).
    • Later: ↑ Heart Rate (HR) by 15-20 bpm.
  • Blood Volume:40-50%.
    • Plasma volume ↑ 40-50% > RBC mass ↑ 20-30% → physiological anemia.
  • Systemic Vascular Resistance (SVR): ↓ (progesterone, PGs).
  • Blood Pressure (BP):
    • Systolic: Slight ↓ or stable.
    • Diastolic: ↓ (nadir mid-preg), then ↑.
  • Heart Sounds: Wide S1 split, S3. Systolic ejection murmur (flow, ~90%). Diastolic = PATHOLOGY.
  • ECG: Left axis deviation.
  • Supine Hypotension: IVC compression → ↓CO. Use left lateral position.
  • 📌 Mnemonic: CO ↑, Blood Volume ↑, SVR ↓, Diastolic BP ↓.

    ⭐ Cardiac output increases by 30-50% during pregnancy, peaking around 20-24 weeks. Maternal Physiological Changes in Pregnancyoka

Maternal Physiological Changes - Breathing & Peeing

Respiratory System:

  • Diaphragm: Elevated ~4 cm; Thoracic cage circumference ↑.
  • Tidal Volume (TV) & Minute Ventilation (MV): ↑ 30-50%.
  • Functional Residual Capacity (FRC) & Residual Volume (RV): ↓ 20%. Total Lung Capacity (TLC) slightly ↓.
  • $PaCO_2$: ↓ to 27-32 mmHg (progesterone effect) → compensated respiratory alkalosis.
  • Physiological dyspnea common.

Lung Volumes: Pregnant vs Non-Pregnant

Renal System:

  • Kidneys: ↑ size; Glomerular Filtration Rate (GFR) & Renal Plasma Flow (RPF) ↑ by ~50%.
  • Serum Creatinine & Blood Urea Nitrogen (BUN): ↓.
  • Physiological hydronephrosis & hydroureter (Right > Left common).
  • Glycosuria: Common (↓ tubular reabsorption of glucose).
  • Urinary frequency & nocturia. Renin-Angiotensin-Aldosterone System (RAAS) activity ↑.

⭐ Progesterone is the primary stimulant for increased minute ventilation, leading to chronic compensated respiratory alkalosis with renal bicarbonate excretion.

Maternal Physiological Changes - Blood & Guts Shifts

  • Blood Volume & Composition:
    • Plasma volume ↑ by 40-50%; Red Blood Cell (RBC) mass ↑ by 20-30%.
    • Physiological anemia: Hemoglobin (Hb) ↓ (e.g., < 11 g/dL in 1st trimester, < 10.5 g/dL in 2nd).
    • White Blood Cell (WBC) count (leukocytosis) ↑; Platelets may slightly ↓.
    • Hypercoagulable state: Fibrinogen ↑, Clotting Factors (VII, VIII, X) ↑. Erythrocyte Sedimentation Rate (ESR) ↑.
    • Iron requirement ↑ significantly (total ~1000 mg).
  • Gastrointestinal System:
    • Nausea & Vomiting of Pregnancy (NVP): Common, linked to hCG.
    • ↓ Lower Esophageal Sphincter (LES) tone → Heartburn/GERD (progesterone effect).
    • ↓ GI motility → Constipation, ↑ nutrient absorption time.
    • Gallbladder: Stasis, ↓ contractility → ↑ risk of cholesterol gallstones.
    • Liver: Alkaline Phosphatase (ALP) ↑ (placental origin); serum albumin ↓ (hemodilution).

⭐ Plasma volume expansion significantly exceeds red cell mass increase, causing physiological hemodilution and a decrease in hemoglobin concentration, hematocrit, and red blood cell count.

Causes of Constipation

Maternal Physiological Changes - Hormones & Body Mods

  • Hormones:
    • hCG: Peaks 8-10 wks; maintains corpus luteum.
    • Progesterone (↑): Smooth muscle relaxation; supports pregnancy.
    • Estrogen (E3) (↑): Uterine/breast growth.
    • hPL/hCS (↑): Anti-insulin (↑ maternal glucose); lipolysis.
    • Relaxin (↑): Softens cervix, ligaments.
    • Prolactin (↑): Prepares lactation.
    • Cortisol (↑), Aldosterone (↑).
    • Thyroid: ↑TBG → ↑Total T4/T3. hCG may ↓TSH (1st trim).
  • Body Modifications:
    • Weight Gain: Avg. 11-16 kg.
    • BMR: ↑ 15-20%.
    • Insulin Resistance: hPL, progesterone, cortisol driven.
    • Breast: ↑Size, tenderness; Montgomery's tubercles; colostrum (~16 wks).
    • Skin: Hyperpigmentation (linea nigra, melasma); striae; spider angiomata. Development of striae gravidarum in pregnancy

⭐ hPL (Human Placental Lactogen) is key for diabetogenic state of pregnancy, ensuring fetal glucose supply.

High‑Yield Points - ⚡ Biggest Takeaways

  • Cardiac output30-50%; SVR ↓; supine hypotension common.
  • Plasma volume ↑ more than RBC mass, causing physiological anemia; hypercoagulable state.
  • Tidal volume & minute ventilation ↑; PaCO2 ↓ (compensated respiratory alkalosis).
  • GFR & renal plasma flow ↑ by 50%; mild proteinuria & glycosuria can be normal.
  • Estrogen, progesterone, hCG, hPL; progressive insulin resistance.
  • Uterine blood flow ↑ dramatically.
  • Diaphragm elevated, AP chest diameter ↑; thoracic breathing predominates.

Practice Questions: Maternal Physiological Changes

Test your understanding with these related questions

Compared to a pregnant female, a lactating female would require a higher level of nutrient supplementation for which of the following?

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Flashcards: Maternal Physiological Changes

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Is Pansystolic murmur normal in pregnancy?_____

TAP TO REVEAL ANSWER

Is Pansystolic murmur normal in pregnancy?_____

No

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