Fetal Hydronephrosis: A Narrative Review of Diagnostic Pathways, Prognostic Markers, and Management.

Fetal hydronephrosis is the most frequently detected prenatal urinary tract abnormality and encompasses a broad clinical spectrum, ranging from transient physiological dilation to clinically significant obstructive uropathy with potential long-term renal consequences. The broader term urinary tract dilation integrates renal pelvic and calyceal dilation with abnormalities of the renal parenchyma, ureters, bladder, and amniotic fluid volume, thereby supporting more comprehensive risk stratification. This narrative review synthesizes evidence on fetal urinary tract development, prenatal diagnosis, contemporary classification systems, differential diagnosis, prenatal intervention, postnatal evaluation, management, and long-term outcomes. Particular emphasis is placed on the transition from isolated renal pelvic measurements to multidimensional assessment using the Urinary Tract Dilation classification system, serial imaging, parenchymal findings, and functional evaluation. Most infants with isolated low-risk dilation experience spontaneous improvement or resolution and can be managed conservatively, whereas severe, bilateral, progressive, or complex abnormalities require structured prenatal and postnatal surveillance, selective use of voiding cystourethrography and radionuclide renography, and, in some cases, surgical intervention. Fetal magnetic resonance imaging and urinary or amniotic fluid biomarkers may provide additional information in selected cases; however, biomarkers remain investigational and should not independently guide clinical decisions. Current evidence supports an individualized, risk-based approach that balances early identification of clinically significant obstruction with avoidance of unnecessary investigations and treatment in self-limiting cases.