Separation of the renal pelvis during fetal life is the separation of the kidney from the ureter. Separation of the renal pelvis is caused by stones or malformations of the ureter, which prevents the normal drainage of urine, and the renal pelvis becomes enlarged, and separation of the renal pelvis can occur when the fetus holds in its urine, and the separation of the renal pelvis, if it is not more than 10 mm, is within the normal range on ultrasound. If the separation of the renal pelvis is relatively large, or if there is a tendency for the pelvis to continue to increase in size, specific treatments should be considered, such as transuterine catheterization to reduce the hydronephrosis. In addition, 90% of babies with renal pelvis separation are male. Some babies may be able to urinate once at birth, but some babies may need surgery to solve the problem due to congenital urinary tract factors. Prenatal diagnosis is needed to rule out chromosomal problems.