Bilateral renal agenesis is typically diagnosed using prenatal ultrasound. Normally the fetal kidneys can be visualized starting at approximately the twelfth week of gestation. In bilateral renal agenesis, however, no renal parenchyma can be visualized either in the normal renal fossae or other ectopic locations, such as the fetal pelvis or thorax. The fetal adrenal glands are in normal position but may appear less flattened because of the lack of normal compression from the kidneys. Finally, the fetal bladder appears empty, and the normal cycles of filling and emptying are not seen.

Severe oligohydramnios is a major consequence of bilateral renal agenesis and may be one of the more notable sonographic findings. Before 20 weeks of gestation, diffusion of fluid into the amnion produces a significant fraction of the amniotic fluid, which therefore may appear normal in volume even despite a lack of fetal renal function. After 20 weeks, however, the fetal kidneys are responsible for producing over 90% of the amniotic fluid. Severe oligohydramnios at this stage of development is therefore a very sensitive sign of bilateral agenesis. It is not, however, particularly specific, and other possible causes—including bilateral renal dysplasia, bilateral renal cystic disease, urinary outflow tract obstruction, premature rupture of membranes, and fetal demise—must be ruled out.