According to the mechanism of hydrocele and its prognosis, it is generally classified into: 1. physiological hydrocele: it accounts for most of the hydrocele in fetus, and most of them can subside on their own without any adverse effects on growth and development. 2. 2. Pathological fetal hydronephrosis: it is caused by the separation of the fetal pelvic collecting system due to real obstructive factors, the most common cause is obstruction at the ureteropelvic junction. Other obstructions such as ectopic ureteral cysts and vesicoureteral reflux can also cause obstruction. Pathological hydronephrosis does not heal spontaneously and affects the renal function of the child, requiring medical intervention. Common diagnostic criteria for the evaluation of fetal hydronephrosis: Grigo five-level classification (20 weeks of gestation) 1, level 1: renal pelvis dilated less than 1 cm, normal renal calyces; 2, level 2: renal pelvis dilated 1-1.5 cm, normal renal calyces; 3, level 3: renal pelvis dilated greater than 1.5 cm, mildly dilated renal calyces; 4, level 4: renal pelvis dilated greater than 1.5 cm, moderately dilated renal calyces; 5, level 5: renal pelvis dilated Greater than 1.5 cm, severe dilatation of the renal calyces, and thinning of the renal parenchyma.