The kidneys increase in size 1.5 cm because of the increase in renal blood
flow; this hypertrophy does not reverse until three months postpartum.
Ureteral diameter increases owing to the progesterone effect on smooth
muscle; the right side dilates more than the left in 90% of patients.
Glomerular filtration rate (GFR), renal plasma flow, and creatinine
clearance all increase by 50% as early as the end of the first trimester; this
causes a 25% decrease in serum blood urea nitrogen (BUN), creatinine, and
uric acid.
Urine glucose normally increases; glucose is freely filtered and actively
reabsorbed, although the tubal reabsorption threshold falls from 195 to 155
mg/dL.
Urine protein remains unchanged