2 The procedure

2.1 Indications

2.1.1 Fetal lower urinary tract outflow obstruction may be associated with various developmental abnormalities. Lower urinary tract outflow obstruction may develop in a fetus from a number of pathologies, including urethral atresia and posterior urethral valves, and can be partial or complete. Severe obstruction may lead to oligohydramnios (that is, a reduction in amniotic fluid volume) and abnormal development of the lungs and kidneys (pulmonary and renal dysplasia). Pulmonary and renal dysplasia may cause death soon after birth from respiratory or renal failure, respectively, or the baby may require ventilatory support, renal dialysis or kidney transplantation. The long-term prognosis for children who require dialysis or transplantation in infancy is poor.

2.1.2 There is uncertainty about the criteria for appropriate selection of fetuses for treatment with vesico–amniotic shunting.

2.1.3 Fetal lower urinary tract outflow obstruction is usually managed expectantly or by repeat vesicocentesis. Some cases are managed by termination of the pregnancy.

2.2 Outline of the procedure

2.2.1 The aim of a fetal vesico–amniotic shunt for lower urinary tract outflow obstruction is to decompress the obstructed bladder and restore amniotic fluid dynamics and volume, thereby preventing oligohydramnios and consequent pulmonary and renal dysplasia. Fetal blood is also sampled for chromosomal analysis to help diagnose or exclude concomitant chromosomal abnormalities that may influence management decisions or treatment choices.

2.2.2 The procedure is performed under maternal local anaesthesia and ultrasound guidance. A cannula on a trocar is inserted through the mother's abdominal and uterine walls into the amniotic cavity and subsequently into the bladder of the fetus. A catheter is inserted through the cannula and positioned with one end in the bladder and the other in the amniotic cavity. The cannula is then removed and the final position of the catheter confirmed by ultrasonography. If the fluid reaccumulates or the catheter is dislodged, the procedure can be repeated.

2.3 Efficacy

2.3.1 A meta-analysis of three controlled trials that compared outcomes following vesico–amniotic shunting (n = 59) with no treatment (n = 33) found that vesico–amniotic shunting was associated with a statistically significant improvement in perinatal survival, with an odds ratio (OR) of 2.53 (95% confidence intervals [CI] 1.08 to 5.93, p = 0.03). Postnatal survival was also better in the vesico–amniotic shunting group, but the results were not statistically significant (OR 2.24, 95% CI 0.89 to 5.59, p = 0.09). In four case series, survival into infancy ranged from 40% (2/5) to 91% (21/23).

2.3.2 In three of the case series, with a maximum of 5.5 years' follow-up, between 25% (2/8) and 33% (2/6 and 6/18) of children required dialysis or underwent renal transplantation. A case series reported renal function as acceptable in 44% (8/18) of infants followed up for a mean period of 5.8 years. Another case series reported good renal function in 75% (6/8) of infants at 1 year's follow-up. One case series reported asthma in 39% (7/18), recurrent pulmonary infections in 28% (5/18) and bladder dysfunction requiring catheterisation in 17% (3/18).

2.3.3 In a case series of 18 children, the mean child self-reported quality-of-life score was 84.2 points at 5.8 years' follow-up, which compared well with a score of 83.0 points in a control population of healthy children, and 77.2 points in chronically ill children in another study. For more details, refer to the 'Sources of evidence' section.

2.3.4 The Specialist Advisers considered vesico–amniotic shunting to be an established procedure but acknowledged that there were limited data to assess its efficacy. They stated that there is uncertainty about selection criteria and about whether the procedure improves outcomes.

2.4 Safety

2.4.1 The evidence on safety came from five case series. The most frequent prenatal complication was shunt displacement, which occurred in 22% (2/9), 28% (5/18) and 60% (9/15) of fetuses and often required insertion of a replacement shunt. One case series reported a single case out of 18 procedures (6%) of premature rupture of the amniotic membranes 4 days after placement of a shunt.

2.4.2 Postnatal complications included one report of bladder prolapse at birth and one report of requirement for intermittent catheterisation. For more details, refer to the 'Sources of evidence' section.

2.4.3 The Specialist Advisers stated that the main potential adverse events for the fetus include preterm labour or spontaneous abortion, shunt blockage or displacement, fetal trauma, fetal hydrops and urinary ascites. Potential complications for the mother include trauma to the maternal organs and infection.