Fetal hydronephrosis is the swelling of the kidney when too much urine collects in the pelvis (or basin) of the kidney. This occurs because there is a blockage of the normally free flow of urine, most commonly in the ureter (the tube that connects the kidney to the bladder), and the urine is not allowed to drain into the bladder. This blockage causes a pressure buildup which causes the kidney to enlarge. The severity of fetal hydronephrosis depends on how large the kidney has ballooned and the extent of the blockage. If not corrected, it can cause the kidney to lose its ability to make urine. True hydronephrosis is, therefore, a major concern.
Fetal hydronephrosis is caused by an obstruction to what should be a free flow of urine out of the kidney. An example of this is kinking of the ureter. It may also be caused by an abnormal backwashing of urine from the bladder back into the kidney. An example of this is vesicoureteral reflux or "reflux."
Hydronephrosis is diagnosed prenatally (before birth) using ultrasound (sonogram) examination. After the baby is born, ultrasound or other tests may be necessary to determine the cause and severity of the hydronephrosis. Tests may include intravenous pyelogram (IVP), voiding cystourethrogram (VCU), renal scan or magnetic resonance imaging (MRI).
There are no outward symptoms to the pregnant mother that her fetus has hydronephrosis. Once the baby is born, the pediatrician may be able to feel a swelling in the region of the kidney (under the angle of the ribs in the back or deep in the mid-abdomen), but many times the newborn examination is normal. Decreased urine flow after birth, swelling that occurs later in the kidney area or urinary infection are other possible symptoms of this problem.
Treatment of fetal hydronephrosis is usually postponed until after delivery. Only in the most severe cases (in which the loss of kidney function is expected if left untreated to delivery) is intrauterine surgery attempted during the pregnancy. In these most severe cases, an attempt is made to place a drain through the baby's back into the kidney to allow passage of urine and relief of the pressure in the kidney.
This is done with endoscopic instruments inserted through mother's abdomen into the uterus (womb) itself. Because of the risks of preterm labor, infection, injury to baby or mother, and poor outcome, this procedure is reserved for the most severe cases.
Less severe cases are treated after delivery, and the kidney usually recovers well and there are no long-term problems. Treatment involves surgery, either major or minor, to correct whatever is causing the blockage of urine or to repair the valve-like structures of the ureter to prevent backflow of urine from the bladder.