What is lower urinary tract obstruction (LUTO)?
Most often, people are born with two kidneys. The kidneys clean the blood and make urine, among other functions. Urine drains from the kidneys into the bladder and then out of the body. During pregnancy, the fetus empties its bladder into the amniotic cavity. After about halfway through pregnancy, the amniotic fluid (the water around the fetus) is made mostly of fetal urine.
When a fetus has lower urinary tract obstruction (LUTO), it can’t normally and routinely empty its bladder. This can result in a decrease in amniotic fluid around the fetus, as well as an increase in bladder volume and pressure in the urinary tract. In severe cases, this can lead to a buildup of urine in the stomach (urinary ascites) or a pocket of urine around the kidney (urinoma).
Differences in kidney and bladder development are the most common causes of chronic kidney disease in children. LUTO occurs in 1 out of every 5,000-8,000 pregnancies. It is nearly always seen in boys, but there are rare cases in which it occurs in girls.
Lower Urinary Tract Obstruction | Symptoms & Causes
What are the symptoms of LUTO?
In most cases, there are no specific symptoms of LUTO during pregnancy, although some pregnant people report decreased fetal movement. The only way to diagnose LUTO is with imaging, such as ultrasound.
In some severe cases of LUTO, there may be low amniotic fluid (oligohydramnios) or none (anhydramnios).
What causes LUTO?
A common cause of LUTO is the presence of extra flaps of tissue in a thin membrane, almost like a tiny blister in the urethra (urine tube that leaves the bladder) that blocks the flow of urine, a condition called posterior urethral valves (PUV)). Other possible causes of LUTO include anterior urethral valves (similar to PUV, but in a different part of the urethra), urethral atresia and/or stenosis (in which a portion of the urine tube does not develop, or ureteroceles (a small balloon-like end of the ureter which falls into the urethra, blocking it). Other conditions that can cause abnormal drainage of urine before birth include prune belly syndrome/Eagle-Barrett, megacystis microcolon intestinal hypoperistalsis syndrome (MMIHS), and cloacal anomalies.
Lower Urinary Tract Obstruction | Diagnosis & Treatments
How is LUTO diagnosed?
LUTO is diagnosed prenatally by ultrasound.
When doctors look at ultrasound pictures of a fetus’ kidneys or bladder, they might also see signs that the kidneys aren’t developing correctly, such as small cysts or an abnormal appearance of the kidney tissue. Swelling of the kidneys (hydronephrosis), a dilated bladder, or a dilated posterior urethra are also signs of LUTO.
Severe cases of urinary tract obstruction can present with oligohydramnios (low volume of amniotic fluid) or anhydramnios (no amniotic fluid). Other prenatal renal ultrasound findings may include increased renal echogenicity and cortical cysts suggestive of renal dysplasia.
Other tests you may encounter include:
How do we treat LUTO at Boston Children’s?
Doctors carefully follow fetuses with LUTO and can often treat LUTO before delivery. It is important to make sure that there’s enough amniotic fluid to help the fetus’ lungs grow and reduce the risk of lung problems. Changes seen in the kidneys can help families know what to expect in terms of kidney function after birth. If the obstruction starts earlier in pregnancy and is severe, there is a lower rate of survival and a higher chance of adverse outcomes.
Treatment for LUTO includes:
- Expectant observation. As with many medical problems, LUTO exists on a spectrum — there are severe cases in which the amniotic fluid is low and lung development is threatened, and mild cases in which the lungs and kidneys develop normally or near-normally. There are many cases in which careful observation is appropriate. The Boston Children’s Maternal Fetal Care Center puts together a team of specialists to develop a care plan for the newborn after delivery if needed, so that everyone is prepared with a plan before birth.
- Fetal therapy to replenish amniotic fluid amounts to allow improved lung development and decrease the rates of pulmonary hypoplasia. This is considered in cases of isolated LUTO (no noticeable structural anomalies) diagnosed with complete PUV obstruction when amniotic fluid is low or absent.
Fetal therapeutic options:
Shunt placement: A shunt is a thin plastic tube that can let fluid move from the bladder to the amniotic sac. This may help restore amniotic fluid volume, but this does not repair kidneys that have developed abnormally. It is common for shunts to fail or require replacement. Newer shunt technology is being developed at Boston Children’s Hospital.
Infusions: Doctors can give the pregnant person infusions of fluid to keep normal amniotic fluid levels until delivery. This is considered experimental, and so far, there is no data that this changes the outcome for the baby. In most clinical trials, the pregnant person requires many infusions (1-3 times per week until delivery), and these interventions may be associated with early deliveries.
Fetal cystoscopy: Considered a diagnostic and therapeutic procedure in specific cases, fetal cystoscopy can be used to diagnose the cause of the obstruction (posterior urethral valves or urethral atresia). Clinical trials in Europe have performed in-utero cystoscopy and PUV ablation with limited data.
Fetal intervention is offered to fetuses with evidence of preserved fetal renal function. The options to determine renal function are limited and include a bladder tap to analyze urine for electrolytes and a follow-up ultrasound to monitor bladder re-filling. We recommended this as a preliminary step in most cases considered for intervention. Moreover, while most cases of LUTO are not associated with a genetic anomaly, we recommend invasive genetic analysis to rule out such pathology as it may change the overall prognosis and outcome.
What is the long-term outlook for LUTO?
The long-term outlook for LUTO depends on the severity of the condition and how far it has progressed. We do know that newborns diagnosed with complete obstruction have significant rates of pulmonary hypoplasia and renal impairment that will require dialysis. Other complications include infections, prune belly syndrome, bladder dysfunctions, and impaired development of joints and musculature. Newborns that survive will likely need to stay in the hospital for a long time and undergo multiple treatments.