[Prenatal ultrasound diagnosis of the kidneys and efferent urinary tract. Possibilities, applications and dangers].

Congenital abnormalities of the urinary tract can be detected as early as during the 15th-18th week of gestation. Nevertheless, most abnormalities are detected between the 28th-30th week of gestation. Antenatal fetal abnormalities vary between physiological dilatation to bilateral hydronephrosis and polycystic kidney disease. Abnormalities in antenatal fetal ultrasonography are found in 0.5% of all pregnancies, 30-50% of these abnormalities are related to the urinary tract. Though most of the abnormalities are diagnosed late in pregnancy, irreversible damage of the kidneys has already taken place by that time and the fetus will not profit from antenatal therapy. On the other hand, a fetus with late onset of urinary tract obstruction may profit from antenatal intervention or early labor. Repeated ultrasonography is crucial for initiating further invasive diagnostic procedures, antenatal therapy and for planing the time of labor. There is a great risk of overdiagnosing and inadequate therapy because too little is known about physiological development of the fetal urinary tract in ultrasonography and so physiological and pathological development cannot be differentiated safely.