Cardiovascular Changes in Pregnancy

Pregnancy requires dramatic cardiovascular adaptation to meet increased maternal and fetal metabolic demands. Blood volume: - Increases 40–50% by 32–34 weeks (plasma 50%, RBC 20–30%) - Plasma increases more than RBC mass → physiological anemia of pregnancy (dilutional anemia): Hgb 11–12 g/dL, Hct 33–37% (normal in pregnancy) - Dilutional anemia reduces blood viscosity → improves uteroplacental perfusion Cardiac output (CO): - Increases 30–50% above non-pregnant baseline - Mechanism: increased stroke volume (early) + increased heart rate (15–20 bpm above baseline) - Peak CO: 28–32 weeks - CO further increases 30–45% during labor and 50–60% during pushing Heart rate: - Resting HR increases 15–20 bpm above pre-pregnancy baseline - Normal range in pregnancy: 80–95 bpm (previously tachycardia) Blood pressure: - Systolic: minimal change (slight drop) - Diastolic: decreases 10–15 mmHg in 1st/2nd trimester (progesterone-mediated vasodilation) - BP returns to pre-pregnancy baseline by 3rd trimester - Normal: systolic <120/diastolic <80 (unchanged physiologically) Peripheral vascular resistance: - Decreases 25–30% (progesterone causes smooth muscle relaxation in vessel walls) - Responsible for 1st/2nd trimester BP drop and edema tendency Cardiac changes: - Heart displaced left...