Many cases of low or bilateral obstructive uropathy due to malformations lead to death, either in utero or at birth, as the absence of diuresis leads to oligoamnios, which in turn causes hypoplasia of the lungs that does not allow neonatal survival. The associated chromosomal anomalies or multiple malformations also have harmful effects. These severe prenatal forms had not been taken into account for pediatric statistics, and were previously not studied. Thus it proved essential for prenatal medicine not to be content with arriving at diagnoses, but rather to try and foresee the prognosis of the abnormalities revealed by assessing the renal function of the fetus in each case. A number of data on fetal urine, such as the sodium, 2-microglobulin or calcium levels, make this assessment possible. Correlations between the fetal urinary parameters and the renal function in the child at age one have been established. These criteria now allow distinguishing the fetuses that will not survive from those that will have renal insufficiency and, finally, from those whose renal function will be normal at age 1.