The birth defect known as hydronephrosis is a urinary tract defect in which the flow of urine from the body is obstructed, leading to dilation (enlargement or stretching) or a distension of the kidney with urine backed up from the bladder.
This sometimes causes kidney stones, among other related injuries. The hydronephrosis blockage also can lead to defects of the stomach, heart or spinal cord.
About one in 500 babies is born with this birth defect, and more are male then female.
Most newborn infants suffering hydronephrosis will grow out of the condition within about the first two years of life and may not require treatment. But if the condition persists and kidney function is affected, surgery or other treatment may be needed to remove the obstruction.



