The kidneys are connected to thin tubes called ureters, which carry the urine to the bladder. During early growth and maturation of the kidneys, sometimes conditions develop that may change the way the kidney looks or functions. One such condition is hydronephrosis. See Figure 1. The hydronephrosis depends on the extent of the blockage and the amount of stretching of the kidney.
Hydronephrosis ranges from mild, moderate to severe.
See Figure 2. The cause of the obstruction that produces hydronephrosis is usually a narrowing at the top of the ureter in the portion nearest to the kidney. The cause of this narrowing is not currently known, but probably developed before the fourth month of pregnancy. Hydronephrosis has never been linked to anything parents have done during pregnancy and is usually not passed down from parent to child or found in more than one sibling in a family. Your baby's hydronephrosis was most likely found when you had an ultrasound during your pregnancy or following a urinary infection that your baby has had since birth.