Renal Changes in pregnancy

• The renal system undergoes significant changes to maintain fluid and electrolyte balance, excrete metabolic wastes, and regulate blood pressure during pregnancy



• The main renal changes include:
  • Increased renal blood flow: The amount of blood flowing through the kidneys per minute increases by 50% to 80% during pregnancy. This is due to increased cardiac output and decreased renal vascular resistance. The renal blood flow peaks at mid-pregnancy and then declines slightly until term. The normal range of renal blood flow in pregnancy is 1200 to 1500 mL/min.
  • Increased glomerular filtration rate: The rate at which the kidneys filter blood and produce urine increases by 40% to 60% during pregnancy. This is due to increased renal blood flow and increased glomerular permeability (the ability of the glomeruli or clusters of capillaries in the kidneys to allow substances to pass through). The glomerular filtration rate peaks at mid-pregnancy and then declines slightly until term. The normal range of glomerular filtration rate in pregnancy is 120 to 150 mL/min.
  • Increased urinary output: The amount of urine produced per day increases by 25% to 50% during pregnancy. This is due to increased glomerular filtration rate and decreased tubular reabsorption (the process by which the kidneys return substances from the urine back to the blood). The urinary output peaks at mid-pregnancy and then declines slightly until term. The normal range of urinary output in pregnancy is 1200 to 1500 mL/day.
  • Decreased serum creatinine and urea: The concentration of creatinine and urea in the blood decreases by 25% to 50% during pregnancy. This is due to increased glomerular filtration rate and increased plasma volume. The serum creatinine and urea reach their lowest point at mid-pregnancy and then remain stable until term. The normal range of serum creatinine in pregnancy is 0.4 to 0.8 mg/dL and the normal range of serum urea in pregnancy is 9 to 21 mg/dL.
  • Increased urinary protein: The amount of protein excreted in the urine increases by 50% to 100% during pregnancy. This is due to increased glomerular permeability and increased protein intake. The urinary protein reaches its highest point at term and then returns to pre-pregnancy levels by the postpartum period. The normal range of urinary protein in pregnancy is less than 300 mg/day or less than 1+ on dipstick.
  • Increased urinary glucose: The amount of glucose excreted in the urine increases by 100% to 200% during pregnancy. This is due to decreased tubular reabsorption and increased insulin resistance (the reduced ability of the body to respond to insulin). The urinary glucose reaches its highest point at mid-pregnancy and then declines slightly until term. The normal range of urinary glucose in pregnancy is less than 100 mg/dL or negative on dipstick.
  • The renal changes result in increased renal clearance (the rate at which the kidneys remove substances from the blood) and decreased serum osmolality (the concentration of solutes in the blood) that maintain fluid and electrolyte balance, excrete metabolic wastes, and regulate blood pressure during pregnancy
  • The renal changes may cause symptoms such as frequency, urgency, nocturia (urination at night), or glycosuria (glucose in the urine) that are normal or abnormal depending on the severity, duration, and frequency