Examinations of the kidneys are carried out using three types of computerised graphic windows:

1. '3-scan' method, to study both kidneys from the coronal, sagittal, and transverse plane, in order to evaluate the presence, structure, integration and relationships with the adjoining organs. In the second and third trimesters the tests are particularly useful to evaluate abnormalities of the kidneys and renal pelvis;
2. Three intersecting planes (less useful);
3. 3D rendering: Our group has adopted 3D rendering to study the kidney as part of a speculative study to show the possibility to obtain a 3D rendering of the fetal kidney (although scanning examination results more useful).

The volumetric observation can be undertaken usually on the transverse plane of the two kidneys. Sometimes the position of the fetus does not allow both kidneys to be seen at the same time, in other cases the volumetric observation is limited to the affected kidney. The 3D images of multiplanar ultrasound are compared to those obtained with 2D ultrasound. By means of multiplanar coordinates, the operator may choose to see any point in 3D vision. In our experience the use of volumetric examinations to study the kidneys (particularly using the multiplanar window) increases the definition of the images and thus provides the echographer with a more precise diagnosis.

BLADDER
The fetal bladder, always visible on 2D ultrasound when full, can be highlighted and measured easily with 3D ultrasound. In the adult, the bladder trigon can be seen in 3D, but repeated attempts to observe the fetal bladder trigon were not successful.
The three-dimensional examination shows the bladder on 3 simultaneous orthogonal scans. Its position can be evaluated with respect to the neighbouring organs and distinguished from the pseudocystic pathological formation situated in the ileac hollow (hydrometrocolpus, persistent cloaca, anorectal atresia). The differential diagnosis of ovarian cysts is based on the simultaneous visualisation of the female sex organs, and of bilateral cysts with a transonic content distinct from the bladder.

URETHRA
In male fetuses, the volumetric examinations of the penis show the path of the penal urethra. The fetal penis is shown on all multiplanar scans at the same time, which enables to study the course of the urethra.