Inability to visualize the fetal bladder on targeted prenatal sonography examination. The fetal bladder can be visualized with sonography as a midline, fluid-filled structure in the pelvis as early as 10-12 weeks of gestation. The normal fetus voids at least once an hour but never completely empties the urinary bladder. The fetal bladdder should be consistently imaged after 13 weeks of gestation. [from HPO]