Natural Course of Congenital Hydronephrosis in Infants Aged 0-6 Months

Inclusion Criteria: * Diagnostic Criteria: Congenital hydronephrosis is diagnosed by abdominal ultrasound examination and meets the UTD grading system criteria (Grades I-III). This is defined as an anterior-posterior renal pelvis diameter (APD) ≥4 mm during the fetal period or ≥7 mm after birth, or accompanied by calyceal dilation, renal parenchymal changes, and other manifestations. * Informed Consent: The legal guardian voluntarily agrees to participate in the study and provides written informed consent. * Follow-up Feasibility: The guardian commits to cooperating with the complete 3-year follow-up period, including attending regular examinations at the research center, and maintains stable contact information. Exclusion Criteria: * Presence of other severe congenital malformations that may affect follow-up or prognosis assessment, such as congenital heart disease, biliary atresia, spina bifida, etc. * Secondary hydronephrosis caused by acquired factors (e.g., urinary system tumors, stones, trauma) or well-defined genetic metabolic diseases. * Having received interventional treatments prior to enrollment, such as surgical procedures related to hydronephrosis (e.g., pyeloplasty) or pharmacological interventions (e.g., long-term use of diuretics). * Severe underlying diseases that preclude tolerance for long-term follow-up, such as severe infections, respiratory failure, or renal failure (e.g., glomerular filtration rate \< 30 ml/min/1.73m²). * Inability of the legal guard…