I just had an ultrasound at 33 weeks and my baby (a boy) was diagnosed with hydronephrosis. The doctor said he may need surgery after he's born. Can you tell me more about it? I'm really concerned about a small infant undergoing surgery and I wonder how this condition will affect his kidney function later in life.

You are not alone in your concerns. Hydronephrosis is being detected before birth with greatly increasing frequency. In the recent past, hydronephrosis (an enlargement of the kidneys caused by some degree of blockage to normal urine flow) was uncommon and was usually treated surgically. Most of the cases of hydronephrosis were detected due to either decreased amniotic fluid or decreased urine output after birth. If left untreated, hydronephrosis would cause progressive kidney damage.

Today the situation is entirely different. With an explosion of the number and quality of prenatal ultrasounds, a huge number of children with some degree of hydronephrosis have been discovered. In some studies as many as 1% of children (mostly boys) have been diagnosed with prenatal hydronephrosis.

This sudden increase in the number of cases of hydronephrosis has led to a flurry of controversy and confusion. What is the real significance of this asymptomatic hydronephrosis? How do we know which newborns with hydronephrosis will get worse and which will stabilize or improve? When should we operate on these children, and when should we simply observe them? Which children have hydronephrosis caused by a urine obstruction early in development that has already corrected itself? In which children is there still an obstruction to urine flow? These dilemmas are currently being sorted out.

We do know that about 20-35% of the cases of prenatal hydronephrosis will resolve spontaneously before the child is even born. In one study of children in which the prenatal hydronephrosis persisted after birth, continued follow-up showed that 93% of the children had complete resolution of their hydronephrosis over time -- with no loss of kidney function. Only 7% of those who still had the hydronephrosis after birth went on to have progression of the hydronephrosis and eventually required surgery. Those who did require surgery did not have any permanent loss of kidney function.

The management of children with hydronephrosis is still evolving. Most agree that a repeat ultrasound shortly after birth should be done to assess the progression of the condition. If the hydronephrosis is stable or improving and no current obstruction is identified, most doctors recommend managing the child conservatively with close follow-up and prophylactic antibiotics to prevent kidney infections. Additional specialized imaging studies may be recommended by the urologist to determine the cause of the hydronephrosis, especially if ongoing obstruction is suspected. If at any point an ongoing obstruction is found, or if the hydronephrosis is worsening, surgery may be needed. Thankfully, this surgery is safe and effective.

For your child, one of two situations pertains:

1. Perhaps(probably) your baby has a benign condition that a few years ago never would have been noticed at all, and which will resolve spontaneously. This condition will cause no bigger problem than your short-term worry and concern.
2. On the other hand, (possibly) your child has a hydronephrosis that results from an ongoing obstruction. In this case, finding it early will help to get the needed treatment at the optimum time.

Either way I wish you the best.