The fetal kidneys initially appear as hypoechogenic regions. As pregnancy advances, there is deposition of fat in the perinephric region, and differentiation of cortex from medulla is apparent in most fetuses by 24 weeks.
Amniotic fluid volume assessment is vital.
The fetal bladder can be visualized in all normal fetuses. (The bladder may be empty immediately postmicturition. If the bladder is not seen rescan after an interval.)
·Assessment of urine production- Serial volume measurements of the fetal bladder can give a rough assessment of urine production. Bladder volume bladder dimensions AP X transverse X length X 0.52 (ml).
The fetal bladder normally empties every 30—45 minutes.