Renal Physiology in Pregnancy

Pregnancy produces changes in the circulatory, renal, and urinary collection systems which support the developing fetus. There is physiologic dilatation of the urinary collecting system. There is systemic vasodilation, leading to decreased systemic vascular resistance, increased cardiac output, activation of the renin-angiotensin-aldosterone system, and plasma volume expansion. Renal blood flow and glomerular filtration rate rise, with a resultant fall in the serum creatinine concentration. Urinary excretion of protein, glucose, and amino acids increases. Electrolyte and acid-base alterations include a chronic respiratory alkalosis and mild hypoosmolarity with hyponatremia. This chapter summarizes the mechanisms and clinical implications of these physiologic changes in pregnancy.