With the rapid development and popularity of ultrasound technology, almost all children with hydronephrosis encountered in the clinic are now found during maternity checkups and can be diagnosed by general ultrasound. Some of the fetuses are physiologically hydronephrosis, which will naturally heal without any treatment at all after birth. Generally speaking, if hydrocele is found in a child during a maternity checkup, the doctor will recommend an ultrasound within a week after the birth of the child to compare with the ultrasound results from the maternity checkup. If you find that the renal pelvis is significantly larger than at the time of the last checkup, you should promptly review the ultrasound to confirm the diagnosis. If the anterior-posterior diameter of the renal pelvis reaches 40 mm or even 50 mm, the doctor may consider performing a dynamic renal imaging test to check for damage to the function of the kidney on that side. If the renal pelvis is simply dilated and the kidney is not damaged, there is no urgency in dealing with it. In many children, the anteroposterior diameter of the renal pelvis is even 40 mm, but a nephrogram reveals that the kidney function is not damaged. If the diameter of the renal pelvis is enlarged and exceeds 20 mm, along with extensive dilatation of the renal calyces, this condition must be promptly examined by isotope nephrogram. If the nephrogram results show renal function below 40%, surgery is indicated. In neonates with hydronephrosis, the reliability of the isotope nephrogram results is uncertain due to the immature kidney development of the child at this stage, and the choice of specific treatment plan needs to be based on the ultrasound results and the experience of individual doctors.