[The urinary tract in pregnancy]

Pregnancy is associated with morphologic alterations of the urinary tract, of which physiological ureterohydronephrosis is the most common. Acute pyelonephritis and obstruction by stones are the two most frequent urinary tract diseases of pregnancy. Medical imaging aims at differentiating physiological ureterohydronephrosis from obstruction and at detecting infections. Ultrasonography plays a central role. Limited roentgenographic investigations can be performed during the second and third trimester. Magnetic resonance imaging can be expected to gain more widespread use in the near future.