Pathophysiology
Clinical meaning
Pregnancy involves profound physiological adaptations across virtually every organ system, all orchestrated to support fetal growth and development over approximately 40 weeks of gestation. Understanding these normal adaptations is essential for the practical nurse to differentiate expected changes from pathological findings during prenatal assessments. The cardiovascular system undergoes dramatic changes: blood volume increases by 40-50% (approximately 1.5 liters) to perfuse the growing uteroplacental unit, cardiac output increases by 30-50%, heart rate increases by 10-20 beats per minute, and peripheral vascular resistance decreases due to progesterone-mediated smooth muscle relaxation and increased nitric oxide production. These changes explain the physiological anemia of pregnancy (hemodilution), the sensation of palpitations, and the slight decrease in blood pressure during the second trimester. The respiratory system adapts through progesterone-stimulated increases in tidal volume (30-40% increase) and minute ventilation, creating a mild respiratory alkalosis (PaCO2 approximately 30 mmHg) that facilitates CO2 transfer from the fetal to the maternal circulation. The growing uterus elevates the diaphragm by approximately 4 cm, reducing functional residual capacity. The renal system experiences a 50% increase in glomerular filtration rate (GFR), which lowers...