-Study of the maternal renal changes during pregnancy will enable obstetricians, urologists, pathologists and sonographer to solve problems related to the urinary tract affection during pregnancy, and to recognize the possible pathological changes and to apply these informations to clinical conditions. -Gestational hydronephrosis and hydroureter may be asymptomatic but concern of exposing to urinary tract infection during pregnancy should be born in mind with emphasis on pyelitis and pyelonephritis. -Ultrasonic visualization of a dilated pelvic portion of the ureter or grade III hydronephrosis especially on the left side should suggest the presence of a pathological obstruction and not gestational hydronephrosis. Further investigation has to be done when this situation is encountered during antenatal ultrasound screening. Mild or moderate hydronephrosis in the presence of tapering of the ureter at the level of the iliac vessels, does not necessitate conventional contrast radiography Это и многое другое вы найдете в книге Sonographic Scanning Of Urinary Tract Affection in Pregnancy