Dayton Children’s Hospital

Bladder Outlet Obstruction (BOO)

What is bladder outlet obstruction (BOO)?

Bladder outlet obstruction (also called bladder neck obstruction or BOO) develops during pregnancy. It happens when the tube that exits your baby’s bladder (called the urethra) is completely or partially blocked. Bladder outlet obstruction is more common in males than females. It happens in about 1 in every 4,000 births.

There are two reasons why BOO is a problem. First, the urethra lets the bladder empty into the amniotic space in the womb, contributing urine to the amniotic fluid. A certain amount of amniotic fluid is needed for the baby’s lungs to develop and to cushion the baby. If the urethra is blocked, urine cannot escape the fetal bladder, so there is not enough fluid for the lungs to develop normally. This lung condition is called pulmonary hypoplasia. Babies born with pulmonary hypoplasia have difficulty breathing and may not survive.

The second problem is a blocked urethra may cause the bladder to become very large and swollen, and trapped urine may back up into the baby’s kidneys and permanently damage them. This may require the newborn to need dialysis and eventually a kidney transplant.

How is the condition diagnosed?

The condition is diagnosed during an ultrasound. During the ultrasound, your doctor will see if your baby has an enlarged bladder (it could be larger than your baby’s head), if there is a normal amount of amniotic fluid, and if there are other physical abnormalities. Your doctor might also perform tests to see how the baby’s heart and kidneys are functioning, or if there are genetic causes of the abnormalities. These tests may include an amniocentesis or a cystocentesis (removal of fluid from the bladder).

How is bladder outlet obstruction (BOO) treated?

The blockage has to be corrected before there is irreversible damage to the baby’s kidneys and bladder. Treatment depends on the cause of the blockage, the amount of amniotic fluid and how at-risk your baby could be for developing future problems. Sometimes just draining the bladder by cystocentesis relieves the obstruction and that is all that is required. In other cases the cystocentesis determines there is already too much damage to the baby’s kidneys and additional treatment will not be beneficial.

If your amniotic fluid is at a normal level, we won’t treat the problem until after the baby is born. However, we’ll carefully monitor your baby’s condition throughout your pregnancy. For example, if your amniotic fluid becomes severely low during your last trimester, we might need to induce an early delivery.

If we determine your baby is at risk for developing kidney or lung problems, you might need a more invasive procedure called fetal vesicoamniotic shunting. This is the most common procedure for treating BOO. Your doctor will place a shunt (a hollow tube) through the baby’s skin into the baby’s bladder. The shunt lets the urine drain from the bladder into the amniotic space. This could help improve the baby’s lung development. Other procedures to correct this condition such as fetoscopic surgery and open fetal surgery have been attempted; however they have many risks and have not been found to be beneficial.

How will bladder outlet obstruction (BOO) affect my baby during and after surgery?

You and your baby will be monitored very closely until the baby is born. This will consist of ultrasound examinations at least every four weeks and often more frequently. During these ultrasounds the condition of your baby’s kidneys, bladder, lungs, and amniotic fluid will be carefully assessed. While you are still pregnant, we will help you arrange consultations with a neonatologist, pediatric urologist and pediatric nephrologist who will discuss the treatment needs and prognosis of your baby after he/she is born. Our team of specialists will help you make a delivery plan that is best for you and your baby. In most instances, your labor and delivery will be normal, but we will prepare to give your baby special attention immediately after birth.

As soon as your baby is born, team members from our newborn intensive care unit (NICU) will be with you to care for your baby. In the NICU, our goal is to monitor your baby for any potential lung, bladder or kidney problems. Neonatologists, pediatric urologists and nephrologists will assess the baby’s condition and consider next steps. Your baby will need diagnostic tests (special x-rays and blood tests) to determine how well the kidneys are working and possibly surgery to correct the blockage. In the meantime, a catheter (small tube) will be placed through the urethra into the bladder to drain urine and relieve pressure on the kidneys.

In the most severe cases of BOO the kidneys function poorly and toxins cannot be removed from the body through urination. These babies could need dialysis and eventually a kidney transplant.

If your baby has lung involvement, he or she could require assistance breathing. Some babies require only extra oxygen while others who have more significant breathing problems will need a breathing tube and mechanical ventilation (a breathing machine).