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In recent years, better ultrasound machines have allowed your doctor to see your baby’s kidneys more clearly during pregnancy. Different types of problems can be found including the absence of one or both kidneys, abnormal position of a kidney, hydronephrosis (swelling of a kidney), fluid-filled cysts and tumors.

The following overview of the urinary tract will help you understand the problems your baby may have.

What does the urinary tract do?
The main function of the urinary tract is to remove wastes and fluid from the body. The urinary tract has four parts: the kidneys, the ureters, the bladder and the urethra. The urine is formed when the kidneys filter blood and remove excess waste materials and fluid. The urine collects into a part of the kidney called the renal pelvis. From the renal pelvis, the urine travels down a narrow tube called the ureter into the bladder. The bladder slowly fills up with urine, which empties from the body through another small tube called the urethra.

During pregnancy, the baby floats in the amniotic fluid within the mother’s womb. This fluid is composed mostly of urine made by the baby. If not enough urine is being produced, there may not be enough amniotic fluid.

What types of problems can happen to the urinary tract in the baby?
Birth defects can occur in any part of the urinary tract. For example:

  • The kidneys may be missing or in a wrong position.
  • A blockage of the outflow of urine or reverse flow of urine already in the bladder (called reflux) can cause the renal pelvis to become enlarged. This is usually called hydronephrosis.
  • A blockage of the urethra can affect emptying of the bladder, causing the pressure in the bladder to be greater. This places extra pressure on the renal pelvis in both kidneys and on the ureters, which can dilate. In boys, the most common blockage of the urethra is called urethral valves.
  • Two ureters can drain a single kidney. In some cases, the connections can be abnormal and hydronephrosis or reflux can be a problem.