Maternal physiological adaptations to pregnancy

Cardiovascular System - Heart's New Roommate

• Cardiac Output (CO) ↑ 30-50%:
  • Driven by ↑ Stroke Volume (SV) early on, then ↑ Heart Rate (HR) by 10-20 bpm.
  • $CO = HR \times SV$. Most of the rise occurs by mid-pregnancy.
• Blood Volume ↑ ~45%:
  • Plasma volume ↑ more than RBC mass ↑ → physiological dilutional anemia.
• Systemic Vascular Resistance (SVR) ↓:
  • Progesterone & prostaglandins cause vasodilation.
  • Leads to ↓ Blood Pressure (BP), reaching a nadir in the 2nd trimester.
• Physical Findings:
  • Hyperdynamic state: systolic flow murmurs, possible S3.

⭐ Supine Hypotensive Syndrome: In late pregnancy, the gravid uterus can compress the inferior vena cava (IVC) when supine, reducing venous return and CO. Advise left lateral decubitus position.

Hematologic System - Blood's Big Gulp

• Plasma Volume Expansion: ↑↑ by ~50%.
• Erythrocyte (RBC) Mass: ↑ by ~20-30% (stimulated by erythropoietin).
• Physiologic Dilutional Anemia: Plasma volume increase is greater than RBC mass increase, leading to a ↓ in hemoglobin/hematocrit.

• Hypercoagulable State: ↑ pro-coagulants (fibrinogen, factors VII, VIII, X) & ↓ anticoagulants (Protein S). This protects against peripartum hemorrhage but increases risk for DVT/PE.
• Other Changes:
  • Mild neutrophilia (↑ WBC).
  • Platelet count may slightly ↓ (gestational thrombocytopenia).

⭐ Pregnancy is a prothrombotic state. The increase in fibrinogen is the most significant factor contributing to the elevated Erythrocyte Sedimentation Rate (ESR) seen in normal pregnancy.

Respiratory & Renal - Breathing & Peeing for Two

• Respiratory System: Progesterone stimulates central respiratory centers.

  • ↑ Tidal Volume (TV) & Minute Ventilation → ↑PaO₂.
  • ↓ Functional Residual Capacity (FRC) from uterine elevation of the diaphragm.
  • Chronic compensated respiratory alkalosis: ↓PaCO₂, ↑pH, ↓HCO₃⁻.

  ⭐ Progesterone-induced hyperventilation facilitates CO₂ diffusion from the fetus to the mother across the placenta.

• Renal System: Increased metabolic demand & fluid volume.

  • ↑ GFR & Renal Plasma Flow by ~50% → ↓ serum BUN & Creatinine.
  • ↑ Renin-angiotensin-aldosterone system activity → ↑ Na⁺ & H₂O reabsorption.
  • 📌 Pregnancy's Progesterone Pushes out PCO₂ & makes you Pee more!

Endocrine & Metabolic - Hormone Havoc

• hCG: Secreted by syncytiotrophoblast; maintains corpus luteum in early pregnancy, mimics TSH.
• Progesterone: "Pro-gestation"; ↑ smooth muscle relaxation (↓BP, constipation), maintains endometrium.
• Estrogen: ↑ uterine/breast development, ↑ prolactin. ↑ binding globulins (TBG, CBG).
• Human Placental Lactogen (hPL): Induces maternal insulin resistance → ↑ glucose & free fatty acids for fetus.
• Pituitary & Thyroid: Pituitary enlarges (↑prolactin). Estrogen ↑ TBG → ↑ Total T4/T3 (Free levels normal).
• Metabolic: Gestational diabetes physiology. Maternal insulin resistance ensures fetal glucose supply.

⭐ hPL (human placental lactogen) creates a diabetogenic state by inducing maternal insulin resistance, shunting glucose to the fetus.

High‑Yield Points - ⚡ Biggest Takeaways

• Cardiac output and plasma volume ↑ significantly, while systemic vascular resistance and blood pressure ↓.
• Dilutional anemia occurs because plasma volume ↑ more than red cell mass.
• Pregnancy is a hypercoagulable state due to ↑ clotting factors, increasing thromboembolism risk.
• Tidal volume ↑, leading to a compensated respiratory alkalosis.
• GFR and renal plasma flow ↑, causing a ↓ in serum BUN and creatinine.