Electrolyte homeostasis in pregnancy: from physiological adaptations to clinical disturbances - a nephrologist's...

Electrolyte homeostasis in pregnancy undergoes several important remodellings driven by systemic vasodilation, activation of neurohormonal pathways, increased glomerular filtration, altered tubular transport, and active maternal-fetal mineral exchange. These coordinated adaptations enable plasma volume expansion, maintain uteroplacental perfusion, and support fetal growth, yet they narrow compensatory reserves and shift normal biochemical reference thresholds. As a result, reliance on non-pregnant laboratory norms can misclassify abnormalities, delaying recognition of clinically important disturbances. Understanding pregnancy-specific physiology is therefore essential for accurate diagnosis, monitoring, and therapeutic decision-making. This review provides an integrated nephrology-focused synthesis of normal adaptive mechanisms and disorder-specific pathophysiology across sodium-water, potassium, magnesium, and calcium balance. We summarize expected gestational changes, including the reset osmostat and AVP-mediated free-water retention causing a physiological fall in serum sodium, changes in potassium homeostasis and magnesium homeostasis, and the doubling of intestinal calcium absorption driven by increased calcitriol to meet third-trimester skeletal mineralization. We further review common clinical disorders of water and sodium, potassium, calcium, and magnesium. The review provides a comprehensive pregnancy-specific interpretation of electrolyte values, diagnostic evaluation strategies, and targeted management tailored to maternal and fetal safety aimed at improving clinical vigilance and optimizing outcomes.