During a routine prenatal examination with 4D ultrasound, the ultrasound report describes a fetus without separation, which is a common term used in ultrasonography, meaning that it indicates that the renal pelvis is not dilated, that is, no hydronephrosis is found and the kidneys are normal. In clinical diagnosis, it is allowed that the normal fetal kidney can have mild separation of the collecting system, and as long as the diameter of separation does not exceed 6mm, it is normal. With increasing gestational age, hydronephrosis can also occur due to expansion of the calyces, which usually disappears on its own and is a normal phenomenon that does not require concern.