Bladder Outlet Obstruction

Bladder outlet obstruction, also referred to as lower urinary tract obstruction (LUTO), is a rare birth defect characterized by a partial or complete blockage in the urethra, the tube that allows the bladder to empty into the amniotic sac.

What is Bladder Outlet Obstruction?

Bladder outlet obstruction, also referred to as lower urinary tract obstruction (LUTO), is a rare birth defect characterized by a partial or complete blockage in the urethra, the tube that allows the bladder to empty into the amniotic sac.

There are several types of bladder outlet obstruction, including:

  • Urethral atresia: a complete obstruction of the urethra (Most common cause in female fetuses)
  • Posterior urethral valves: an abnormal flap of tissue in the urethra blocks the flow of urine (occurs only in male fetuses)
  • Triad syndrome: a constricted mid-portion of the urethra, which makes it difficult for urine to easily pass through. 

Bladder outlet obstruction affects about 1 in 4,000 to 5,000 births and is more common in males.

What are the Signs and Symptoms of Bladder Outlet Obstruction?

A blockage in the lower urinary tract can reduce urine drainage to the outside of the fetus and consequently, the level of amniotic fluid, endangering the baby’s health and development. This obstruction can lead to back up of urine, resulting in progressive bladder damage, kidney damage, increased risk of kidney failure, and deformities of the face and extremities in a condition known as Potter’s sequence. The most serious consequence of little or no fluid around the fetus is underdevelopment of the fetal lungs, a life-threatening condition.

What Causes Bladder Outlet Obstruction?

The cause is unknown, but some cases of bladder outlet obstruction are caused by a genetic or chromosome disorder, while other cases are random and result from abnormally formed tissues or structures.

How is Bladder Outlet Obstruction Diagnosed?

Bladder outlet obstruction is typically diagnosed by an ultrasound examination during the second trimester of pregnancy, although it can be detected, less commonly, at the end of the first trimester. Routine imaging may show an enlarged fetal bladder, thickened bladder wall, swelling of the kidneys, and/or a low level of amniotic fluid. On ultrasound, the dilated bladder and upper part of the urethra can be found to make a keyhole impression (the “keyhole” sign) often used to describe lower urinary tract obstruction due to posterior urethral valves.

If the condition is suspected, your physician may refer you to a fetal center for a comprehensive evaluation and or order additional testing, including:

  • Anatomy ultrasound: a high-resolution ultrasound to confirm the diagnosis, assess the size and condition of the bladder, ureters, kidneys, and identify any other physical abnormalities.
  • Fetal MRI: a non-invasive imaging technique to help provide additional details of the baby’s organs that may not have been visualized on ultrasound. A fetal MRI will be helpful to determine the degree of obstruction.
  • Fetal echocardiogram: a specialized ultrasound to evaluate the baby’s heart structure and function.
  • Amniocentesis: A medical procedure in which a small sample of the amniotic fluid that surrounds the baby in the womb is extracted and studied in the lab and tested for genetic abnormalities. The results could affect the treatment and overall outcomes.  Also, amniocentesis can be used to confirm results of screening using cell-free fetal DNA.
  • Cell-Free Fetal DNA:  Your doctor can take a sample of your blood to look for copies of fetal (baby) DNA.  This is only a screening test. A positive result means that there could be problems with the DNA.  This should be confirmed with another test to be sure of the result.
  • Fetal bladder tap: the extraction of a urine sample to evaluate kidney function.

Advanced testing allows a complete, thorough assessment and helps your baby’s medical team develop recommendations for treatment.

What are the Treatment Options for Bladder Outlet Obstruction?

Treatment depends on the severity of the obstruction and its effect on your baby’s kidneys and amniotic fluid. If the blockage is minor and there is a sufficient level of amniotic fluid, close monitoring of amniotic fluid volume may be the only course of treatment. Other obstructions may be more serious but not life-threatening, warranting surgery after the baby is born.

When the blockage is severe, and tests indicate that the kidney damage is potentially reversible, your doctor may recommend fetal treatment. This option is only available to babies most likely to benefit from intervention, as determined by the results of a comprehensive evaluation. Procedures are designed to restore amniotic fluid volume, promote lung development, preserve kidney function, and ultimately improve your baby’s chance of survival after birth.

How is Bladder Outlet Obstruction Treated During Pregnancy?

The most common fetal intervention is called fetal bladder shunting, which involves placing a tiny, flexible tube, or shunt, in the fetus’ bladder. One end of the tube remains in the bladder while the other opens into the amniotic sac. Shunting allows urine to bypass the blockage and drain from the fetal bladder into the amniotic sac, increasing the amount of fluid in the amniotic sac to allow for proper lung development. While the procedure may relieve pressure on the bladder and kidneys, kidney function is not always preserved.

This minimally invasive procedure is performed in the hospital under sedation. Using ultrasound guidance, the surgeon inserts a hollow needle through the mother’s abdomen and uterus to place the shunt into the fetal bladder. You and your baby will be closely monitored following surgery and throughout the pregnancy to ensure that the shunt remains situated and functioning. Typically, the tube is not removed until the baby is born. 

Less common fetal interventions include:

  • Vesicocentesis (bladder tap): A needle is placed into the fetal bladder to remove the urine. The procedure may be done once or multiple times.
  • Fetal cystoscopy: A tiny, surgical camera is inserted into the fetal bladder to remove the obstruction and restore urine flow.

Each of these procedures involves risks and possible complications, including premature labor or delivery. Treatment is not always successful; children with this condition may endure permanent kidney or lung damage.

Will This Birth Defect Impact my Delivery?

Babies diagnosed with bladder outlet obstruction should be delivered in a hospital that is prepared and equipped to treat babies with rare birth defects. Newborns need immediate access to an experienced team of pediatric specialists, a neonatal intensive care unit (NICU), and pediatric surgical services.

Pre-term or Cesarean deliveries are not necessary unless the fetus shows signs of distress or they are warranted for obstetrical reasons. However, a well-coordinated birth plan is essential, incorporating the expertise of your perinatologist, neonatologists, pediatric nephrologists, pediatric urologists and other specialists as might be indicated, to ensure the best possible outcome.

Will my Baby Require Treatment After Birth?

After birth, a team of neonatologists, pediatric urologists and pediatric nephrologists will thoroughly evaluate your baby’s condition. The initial critical assessment is the lung function.  How developed the baby’s lungs are, and how well they function, will influence subsequent management. Imaging procedures, such as renal ultrasound, blood and urine tests are typically performed within 24 hours of delivery to help them assess your child’s kidney and lung function before recommending a plan of care. Additional imaging tests, such as a voiding cystourethrogram (VCUG), may be employed to evaluate for other associated anomalies such as vesicoureteral reflux (VUR).

Postnatal treatment depends on the type of urinary obstruction and how well the kidneys are functioning. Options may include:

  • Endoscopic resection: Posterior urethral valves can be treated with this minimally invasive procedure to remove the tissue causing obstruction.
  • Vesicostomy: In more complicated cases, this procedure allows urine to exit the body through an opening below the belly button (into a diaper). A vesicostomy is often a temporary solution until your baby is strong and healthy enough to undergo reparative surgery.
  • Dialysis and/or Transplant: Some babies with poor renal function may require ongoing renal replacement therapy or kidney transplant when appropriate.

Your child may spend several weeks, or even months, in the neonatal intensive care unit. The duration of stay will depend on lung development, kidney function, and treatment.

Will Bladder Outlet Obstruction Affect the Long-term Health of my Baby?

Children born with bladder outlet obstruction are at higher risk for kidney infections and kidney failure. Some may experience long-term breathing problems, bladder dysfunction, stunted growth and development, and/or musculoskeletal problems.

Your baby will remain under the care of a pediatric urologist, a pediatric nephrologist and other specialists, who will continue to monitor his or her health.