What changes take place in the kidney during pregnancy?
The kidney undergoes anatomic and physiologic changes during normal pregnancy. The length of the kidney increases by 1 to 1.5 cm and there is hormonally mediated dilatation of the collecting system to a volume of about 300 cc.
The resulting physiologic hydronephrosis makes it difficult to diagnose obstruction by ultrasound. The glomerular filtration rate increases by 50% during the first trimester so that the serum creatinine is expected to be 0.5 to 0.7 mg/dL.
Pregnancy is also characterized by a reset osmotstat where the serum sodium is normally in the range of 134 mEq/L, but a water load can be excreted normally. Additionally, pregnancy is characterized by respiratory alkalosis with a compensatory drop in bicarbonate, making the normal bicarbonate in pregnancy 18 to 20 mEq/L.
