Pathophysiology
Clinical meaning
Pregnancy induces profound physiological adaptations across all maternal organ systems to support fetal development and prepare for parturition. The cardiovascular system undergoes a 40-50% increase in blood volume through plasma expansion (driven by RAAS activation and aldosterone-mediated sodium retention) with a relatively smaller increase in red blood cell mass, producing the physiological anemia of pregnancy. Cardiac output increases 30-50% through elevated heart rate (10-20 bpm above baseline) and increased stroke volume, while systemic vascular resistance decreases due to progesterone-mediated smooth muscle relaxation and the low-resistance uteroplacental circulation. Human chorionic gonadotropin (hCG), produced by the syncytiotrophoblast, maintains the corpus luteum during early pregnancy until the placenta assumes progesterone production at approximately 8-10 weeks gestation.