What renal and urinary changes occur in pregnancy?

Renal plasma flow and glomerular filtration rate increase ~50%, lowering serum urea, creatinine and uric acid, and causing physiological glycosuria (reduced tubular reabsorption).

Progesterone and the uterus cause physiological hydronephrosis/hydroureter (right > left) and urinary stasis (predisposing to UTI/pyelonephritis), with increased urinary frequency.

Clinical relevance. The increased GFR alters renal reference ranges, and urinary stasis predisposes to UTI - so asymptomatic bacteriuria is treated.

More Detail

Renal and urinary changes

Pregnancy markedly increases renal blood flow and alters the urinary tract.

Functional changes

• Renal plasma flow and GFR increase by ~50% (driven by increased cardiac output and vasodilation).
• This lowers serum urea, creatinine and uric acid (so non-pregnant 'normal' values may be abnormal).
• Physiological glycosuria - the filtered glucose load exceeds tubular reabsorption.
• Mild proteinuria and increased sodium/water retention occur.

Anatomical/urinary changes

• Physiological hydronephrosis and hydroureter - progesterone (smooth-muscle relaxation) and uterine compression dilate the collecting system (right > left).
• Urinary stasis predisposes to urinary tract infection and pyelonephritis (and asymptomatic bacteriuria should be treated).
• Increased urinary frequency (uterine pressure on the bladder, increased urine production).