What is lower urinary obstructive uropathy?
diagram of lower urinary
Lower urinary tract obstructive uropathy refers to a blockage in the lower urinary tract, usually below the bladder. The baby is not able to release urine into the amniotic fluid and amniotic fluid levels can become very low. Low amniotic fluid levels (oligohydramnios) impair the developing lungs and causes them to become hypoplastic (small). In addition, severe and prolonged urinary obstruction leads to kidney damage. Babies with little or no amniotic fluid early in gestation (before 24 weeks) have severely underdeveloped lungs and little chance of survival. Those babies that maintain a moderate amount of amniotic fluid do better as their lungs are able to mature. However, the degree of kidney damage and function cannot be fully assessed until after birth.
The most common cause of lower urinary tract obstruction in males is posterior urethral valves. This condition can sometimes be confused with "prune belly" syndrome prenatally. The estimated occurrence is approximately 1 in 5000 live births.
What additional testing is recommended during the pregnancy?
A level II ultrasound will assess for the presence of other anomalies. Serial ultrasounds monitor the presence of amniotic fluid, the bladder, and changes in the appearance of the kidneys. Since bladder outlet obstruction can also be seen in trisomy 13, 18, and 21, a fetal chromosome analysis is recommended.
A fetal echocardiogram is recommended to exclude structural heart defects.
Are there special considerations for the delivery?
Infants born with lower urinary obstructive uropathy require access to a team of pediatric specialists including pediatric nephrologists and pediatric urologists. The birth plan in severe cases of bladder obstruction with oligohydramnios and pulmonary hypoplasia should be discussed in advance. Those infants anticipated to require resuscitation efforts should be delivered at a tertiary care center with a NICU.
Is there fetal treatment for a urinary tract obstruction?
Fetal surgery has been offered to a select group of patients with the goal of restoring adequate amniotic fluid levels to promote sufficient lung development and prevent ongoing kidney damage. Patients who have evidence of oligohydramnios and reversible kidney function are carefully selected. Serial fetal bladder taps, analysis of fetal urinary electrolytes and beta2 microglobulin (a marker of kidney damage), and ultrasound of the fetal kidneys is required to select patients with reversible kidney function. Patients who have evidence of severe irreversible kidney damage are not candidates for fetal intervention.
A vesicoamniotic shunt (a tiny tube from the bladder into the amniotic fluid) can be placed percutaneously (through the skin) into the fetal bladder allowing it to drain. Its effectiveness may be hampered by inadequate drainage of the bladder, and dislodgement or obstruction of the catheter. In select cases, a percutaneous fetoscopic procedure may be performed to ablate posterior urethral valves.
What is the postnatal treatment for urinary tract obstruction?
After the baby is born, a complete evaluation is necessary to accurately determine kidney function and the anatomic obstruction. An individualized diagnostic and treatment plan will be provided by the pediatric nephrologist and pediatric urologist.
Renal ultrasound is a valuable tool for the initial assessment. Babies with severe problems should be scanned within the first day of life. Other tests are performed to assess kidney function. Urine output is assessed and serum blood tests are collected after 24 hours of age.
Babies with severe obstruction require intervention when there is a high-risk of kidney damage. A catheter (tube) can be placed in the urinary tract until a plan for permanent repair is in place.
Are there other health problems that are more common among babies with urinary tract obstruction?
The long-term health of these infants is dependent on factors such as the degree of pulmonary hypoplasia, kidney function and the presence of other malformations. Even with successful fetal intervention, progressive kidney failure is common and may require dialysis or kidney transplantation. Your team of doctors will discuss long-term outcomes with you.
Can this happen again with another pregnancy?
Most cases of bladder outlet obstruction related to posterior urethral valves occur as a random (sporadic) event, without a significant risk of recurrence. Those cases caused by a chromosomal abnormality or by a rare bladder obstruction syndrome have a higher risk of recurrence. Your doctor and a genetic counselor will discuss the risk in your family.