What are urinary tract obstructions?
The urinary system is made up of the kidneys, ureters, bladder and urethra. All of these structures work together to produce urine. The kidneys act as a blood filter to remove excess water and maintain the electrolyte balance in the body. There are usually 2 kidneys which connect to the bladder by the ureters. The bladder holds the urine until the fetus urinates. The urine goes from the bladder through the urethra and passes outside the body. The fetal urine forms the amniotic fluid surrounding the fetus. The amniotic fluid is swallowed by the fetus and is critical for proper lung development.
Depending on the location of the blockage, obstruction of the urinary tract causes a backup of urine into the bladder, ureters, and/or kidneys. This usually results in dilation of these structures that are seen on prenatal ultrasound. There are many causes of urinary tract obstructions but all are due to some sort of blockage that prevents or slows urine from exiting the body. Some of the causes are:
- Bladder outlet or urethral obstructions - The urethra is the small tube that allows the bladder to empty out of the body. Obstructions of the urethra cause a buildup of urine in the bladder. If this is severe, urine can backup into both ureters and kidneys. The most common cause of bladder outlet obstructions is a posterior urethral valve which is an abnormal flap or tissue in the urethra preventing urine from flowing out.
- Bladder inlet or ureterovesical junction obstructions - The ureter is the tube that connects the kidneys to the bladder. This location is called the ureterovesical junction. An obstruction at this level results in a dilation of the ureter and kidney on the affected side. The other kidney and ureter are usually normal. The bladder is usually normal size because the other kidney is still making urine that flows into the bladder.
- Kidney outlet or ureteropelvic junction obstructions - The pelvis of the kidney is the portion that empties urine into the ureter that eventually flows into the bladder. The ureteropelvic junction is the location where the kidney pelvis meets the ureter. Obstructions at this level cause dilation of the collecting tubules of the kidney. This is called hydronephrosis.
- Ectopic ureter - This is abnormal positioning of the ureter as it comes out of the kidney or enters the bladder. This can cause a kinking of the ureter which inhibits urine flow.
- Ureterocele - This is a cyst or other type of structure at the end of the ureter in the bladder that may obstruct the ureter or bladder.
With all of these conditions, the main concern is that blockage of urine may lead to kidney damage. Typically, if only one kidney is affected, the fetus will still do well because the other kidney is fully functional. However, in the most severe cases in which both kidneys are affected, the blocked urinary tract can cause the kidneys to stop functioning and urine production decreases or stops. Decreased urine can cause a decrease in amniotic fluid (oligohydramnios) and impaired lung development. Your physicians will determine the amount of amniotic fluid surrounding the baby by ultrasound evaluation.
How is urinary tract obstruction diagnosed?
Urinary tract obstructions are diagnosed on routine prenatal ultrasound. The ultrasound will show a collection of fluid within the kidney or an enlarged collecting system (bladder, ureter, or kidney). Although the exact location of the blockage may not be determined, ultrasound can help determine the extent of the urinary tract obstruction as well as evaluate the kidney to determine if there is tissue damage and possible loss of function
How is urinary tract obstruction treated?
Once a diagnosis of urinary tract obstruction is made prenatally, your fetus will be closely monitored with ultrasound throughout your pregnancy for changes in the amniotic fluid level, dilation of the urinary system, and changes to the kidney. A targeted ultrasound will be performed to detect associated abnormalities and an amniocentesis may be recommended. If the fetal team becomes concerned that your condition is severe or worsening, further testing may be required including sampling of the fetal urine to test for kidney function. The type of testing performed is dependent on the severity of the condition. For mild hydronephrosis, it may include genetic counseling, amniocentesis, and follow up ultrasound evaluations. Most of these babies do not need to be in a neonatal ICU after delivery. After birth the infant may be evaluated by a pediatric specialist (nephrologist or urologist). Surgery is usually not required for mild cases but a thorough evaluation with additional testing may be necessary after birth. About half of the cases of hydronephrosis diagnosed prenatally will resolve after birth with no further treatment needed.
For severe urinary tract obstruction, such as that caused by posterior urethral valves, additional intervention may be recommended to save the kidneys and/or fetus After a complete evaluation, the fetal team may decide that the best treatment for the fetus would be to insert a catheter or tube into the fetal urinary system to help drain the urine into the amniotic sac. This procedure is similar to an amniocentesis. This scenario is rare and only reserved for the most severe cases.
Your team at the Center will discuss available therapeutic options appropriate for your pregnancy.
What special considerations should be made for delivery?
Type of delivery - Babies with urinary tract obstructions usually do not require cesarean delivery. The delivery plan should be made between mother and her obstetrician.
Place of delivery - Depending on the severity of disease based on prenatal evaluation, your physicians at the Center may recommended that your baby be delivered at a center with all of the capabilities to take care of children with kidney problems and poor lung development such as a neonatal intensive care unit and pediatric surgery. Newborns with mild obstruction can be safely delivered at other facilities.
Time of delivery - Intentional early delivery does not improve outcome. Timing of the delivery should be carefully discussed between the mother and her obstetrician.
What are the long-term outcomes and considerations?
The long-term outcomes of infants that are prenatally diagnosed with urinary tract obstructions depend on the cause and severity of the disease. Although most cases of hydronephrosis resolve without further treatment, the most severe cases can result in kidney failure and abnormal lung development. Depending on the severity, some babies may need corrective surgery. If the fetal lungs do not develop properly, newborns may require assistance with breathing and admission to the neonatal intensive care unit, although sometimes infants with severe lung problems do not survive.
The Center team will help care for you and your infant with urinary tract obstruction. The Center will develop a comprehensive plan with all of the physicians and specialists involved in the care of you and your newborn before, during, and after delivery.
Contact The Fetal Center to make an appointment with a high-risk pregnancy doctor.
Note: This information regarding your condition is meant to be a helpful, informative introduction. Because every newborn is different, this may not be applicable to all cases, especially if there are additional defects. Your team of experts at the Center will provide you with information specific to your pregnancy.