There are two options of fetal treatment in cases of severe lower urinary tract obstructions: the vesico-amniotic shunting and fetal cystoscopy. There is no study confirming the effectiveness of these treatment, specially comparing both techniques. The present study aims to investigate the effectiveness of these treatments.

Objectives: To evaluate the effectiveness of fetal cystoscopy for the diagnosis and therapy of the posterior urethral valves and to compare with the results of vesicoamniotic shunting.

Outcomes: Accuracy of the prenatal cystoscopic diagnosis of posterior urethral valves, neonatal and infant survival (6 and 12 months), as well as normal renal function during the same ages.

Study design: Randomized controlled trial. Methods: Pregnant women whose fetuses have isolated and severe lower urinary tract obstruction (LUTO) with (oligohydramnios and severe hydronephrosis) will be invited to participate in the present study. Patients will be randomized into the fetal cystoscopic group (CYSTO) vs vesico-amniotic shunting (VAS). The investigators intend to enroll 30 patients in each group (a total of 60). All patients will be followed by fetal ultrasound each 15 days. Besides, these infants will be followed up to one year of age. Maternal and obstetrical complications are going to be evaluated as well as neonatal and infant survival and the renal function.

Inclusion Criteria:

• single pregnancy
• male fetuses
• gestational age dating by ultrasound examination performed before 20 weeks
• confirmed severe LUTO (see details before)
• severe oligohydramnios (AFI<5.0cm)
• no other structural anomalies by complete fetal anatomy ultrasound scan and fetal echocardiogram
• no abnormal karyotype
• 'favorable' urine analysis (urinary sodium <100 mEq/L, chloride <90 mEq/L, osmolarity <200 mOsm/L) when gestational age >20 weeks

Exclusion Criteria:

• presence of other anomalies diagnosed after fetal intervention
• maternal refusal to participate in the present protocol