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.
At Boston Children’s Hospital, our Fetal Care and Surgery Center specializes in the evaluation and treatment of LUTO and other complex fetal conditions.
Testing showed Cairo’s bladder and kidneys were enlarged signaling a rare type of lower urinary tract obstruction called posterior urethral valves.
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).
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.
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:
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:
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.
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.
