BACKGROUND: Fetal lower urinary tract obstruction (LUTO) is a rare congenital anomaly in which the bladder cannot empty properly. The clinical presentation is variable. On the severe end of the spectrum, the amniotic fluid index can be sufficiently low, resulting in fetal lung development that is incompatible with life outside the womb. The pressure in the urinary tract system can also result in severe damage to the kidney, resulting in renal failure in utero or in the first couple years of life. Therefore, much work has been done to determine which fetuses need intervention in utero to allow for survival outside of the womb and avoidance of end-stage renal disease. Multiple therapies have been developed to relieve the obstruction in utero with the mainstay being vesicoamniotic shunting and posterior urethral valve ablation.
CONCLUSIONS: While much has been investigated to determine which fetuses would benefit from fetal intervention, the current indications are not without their flaws. This review describes the current indications and their shortcomings, as well as new experimental methods of determining need for intervention. Additionally, this review describes the milestone animal studies that established the challenges of current fetal interventions and the utility of an experimental valved shunt in sheep over the last 20 years.
CONCLUSIONS: Our understanding of LUTO and which fetuses benefit from in utero intervention has grown over the last 20 years. However, traditional markers have proven to be less predictive than previously thought, opening the door to exciting new advances. Vesicoamniotic shunting, while lifesaving, does not preserve bladder function and frequently dislodges. Animal studies over the last 20 years have established the utility of a valved shunt to maintain bladder function. Current advances are working to create such a shunt that can be percutaneously deployed and have greater adherence to the bladder wall to avoid dislodgement.

The aim of this review article is to provide a practical and concise overview of diagnosis and management of pregnancy with fetal lower urinary tract obstruction.
Review of literature and current studies.
Proper diagnosis and management of isolated fetal lower urinary tract obstruction with oligohydramnios allows appropriate implementation of intrauterine treatment in indicated cases. The treatment is a prevention of pulmonary hypoplasia and also improves renal function; this  finally contributes to the improvement of overall perinatal morbidity and mortality.

Fetal lower urinary tract obstruction (LUTO) is classically based on prenatal ultrasound identification of a dilated/ thick-walled bladder, bilateral hydronephrosis, dilated ureters and a dilated posterior urethra (also known as the \"keyhole sign\") in a male fetus. Although the most common underlying diagnosis is posterior urethral valves, the prenatal appearance may be similar with urethral atresia or stenosis, the Prune-Belly Syndrome, or even a cloacal anomaly in a female. These conditions form part of the Congenital Anomalies of Kidney and Urinary Tract (CAKUT) spectrum, which is the commonest cause of end-stage renal disease in children. Although it is difficult to predict postnatal renal function from the prenatal appearance, studies have recently identified predictive features (based on ultrasound findings and fetal biochemistry), and established staging systems to assist with counselling, and, where indicated, patient selection for in-utero intervention. Current in-utero therapy includes amnio-infusion, vesico-amniotic shunting, and fetal cystoscopy with valve ablation or urethral stenting. Postnatal survival and renal functional outcomes, complications and management uncertainties are described, highlighting areas of future development.

OBJECTIVE: In this article, we explore the origins of intervention of fetal lower urinary tract obstruction, and we specifically discuss the background and recent outcomes of vesicoamniotic shunt placement and fetal cystoscopy. The article seeks to provide a comprehensive overview of the field while bringing the reader quickly up to speed on the pertinent literature and the critical data that are available to guide decision-making regarding intervention.
RESULTS: Appropriate patient selection for fetal intervention remains challenging despite advances in prenatal imaging. Both a randomized controlled trial and multiple systematic reviews show evidence of a perinatal survival benefit following fetal intervention but rates of renal morbidity remain very high. Despite 30 years of research, fetal lower urinary tract obstruction remains a difficulty entity to treat. Intervention may lead to survival, but physicians and caregivers must remain alert for the distinct possibility of long-term renal morbidity in survivors.

Fetal bladder outlet obstruction (BOO), most commonly caused by posterior urethral valves (PUV), remains a challenging and multi-faceted condition. Evolving techniques, and refinement in ultrasound, optics and instrumentation, have increased our rate of prenatal diagnosis, and enabled valve ablation not only in smaller newborns, but also in fetuses. Long-term outcome studies have raised our awareness of the silent damage caused by bladder dysfunction and polyuria and encouraged their proactive management. In spite of our best efforts, the proportion of boys with PUV who progress to chronic and end-stage renal disease (ESRD) has not changed in the last 25 years. Evidence suggests a reduction in perinatal mortality following prenatal intervention, probably resulting from amelioration of oligohydramnios at the crucial time of lung development between 16 and 28 weeks\' gestation, but no improvement in postnatal renal outcome. There are no bladder functional outcome studies in patients who have undergone prenatal intervention and hence the long-term effect of in utero defunctionalisation of the bladder is not known. This aim of this review is to revisit the embryopathology of fetal BOO, in particular the renal and bladder structural and functional changes that occur with in utero obstruction. The effect of earlier prenatal diagnosis, and therapy, on postnatal outcome is also explored and compared with outcomes published for traditional postnatal treatment.

Fetal lower urinary tract obstruction (LUTO) encompasses a heterogeneous group of congenital pathologies and generally results in oligohydramnios. Fetal intervention (e.g. vesicoamniotic shunting, fetal cystoscopy) has traditionally been reserved for cases with a favorable renal profile, while those with unfavorable renal function have been offered termination or expectant management with the latter leading to high incidence of marked pulmonary hypoplasia, neonatal morbidity and mortality. Here, we describe two cases, which were not candidates for traditional intervention based on abnormal fetal renal function, who elected to proceed with serial amnioinfusions for fetal pulmonary palliation to attenuate the risk of pulmonary hypoplasia.

OBJECTIVE: To present a single center experience of a standardized prenatal multidisciplinary management protocol for fetal lower urinary tract obstruction (LUTO) and to propose a classification of fetal LUTO based on disease severity.
METHODS: This was a retrospective cohort study of 25 consecutive fetal patients with prenatal diagnosis of primary LUTO. Fetal intervention was offered after evaluation by a multidisciplinary team. Analyses were conducted using Bayesian methodology to determine predictors of survival at 6 months postpartum. Odds ratios (ORs) with 95% credibility intervals are reported.
RESULTS: Fifteen (60.0%) of the 25 patients referred for assessment survived to postnatal evaluation. Fetal vesicoamniotic shunt was placed in 14 (56.0%) patients with 12 survivors. Multivariable analysis suggested that fetal intervention (OR, 6.97 (0.88-70.16), Pr(OR > 1) = 96.7%), anhydramnios (OR, 0.12 (0.04-0.35), Pr(OR < 1) = 99.9%), favorable fetal urine analysis (OR, 3.98 (0.63-25.15), Pr(OR > 1) = 92.7%) and absence of renal cortical cysts (OR, 3.9 (0.66-24.2), Pr(OR > 1) = 93.3%) were predictors of survival.
CONCLUSIONS: Fetal intervention and fetal renal function were independently associated with postnatal survival of fetuses with LUTO. A classification based on the severity of disease is proposed. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.

BACKGROUND: The aim of this study was to identify predictors of \'intrauterine fetal renal failure\' in fetuses with severe congenital lower urinary tract obstruction (LUTO).
METHODS: We undertook a retrospective study of 31 consecutive fetuses with a diagnosis of LUTO in a tertiary Fetal Center between April 2013 and April 2015. Predictors of \'intrauterine fetal renal failure\' were evaluated in those infants with severe LUTO who had either a primary composite outcome measure of neonatal death in the first 24 h of life due to severe pulmonary hypoplasia or a need for renal replacement therapy within 7 days of life. The following variables were analyzed: fetal bladder re-expansion 48 h after vesicocentesis, fetal renal ultrasound characteristics, fetal urinary indices, and amniotic fluid volume.
RESULTS: Of the 31 fetuses included in the study, eight met the criteria for \'intrauterine fetal renal failure\'. All of the latter had composite poor postnatal outcomes based on death within 24 h of life (n = 6) or need for dialysis within 1 week of life (n = 2). The percentage of fetal bladder refilling after vesicocentesis at time of initial evaluation was the only predictor of \'intrauterine fetal renal failure\' (cut-off <27 %, area under the time-concentration curve 0.86, 95 % confidence interval 0.68-0.99; p = 0.009).
CONCLUSIONS: We propose the concept of \'intrauterine fetal renal failure\' in fetuses with the most severe forms of LUTO. Fetal bladder refilling can be used to reliably predict \'intrauterine fetal renal failure\', which is associated with severe pulmonary hypoplasia or the need for dialysis within a few days of life.

We report the case of a fetus with severe megabladder, displaying the \'keyhole\' sign on ultrasound imaging, that underwent cystoscopy at 22 weeks\' gestation. There was a familial history of mild urethral atresia. Fetal cystoscopy revealed congenital urethral atresia. A guide wire was advanced through the fetal urethra and a transurethral vesicoamniotic stent was placed successfully. The fetus was delivered at 36 weeks\' gestation and postnatal cystoscopy confirmed the absence of posterior urethral valves or urethral atresia. The infant was 5 years old with normal renal function at the time of writing. We conclude that fetal cystoscopic placement of a transurethral stent for congenital urethral stenosis is feasible.