Prenatal lower urinary tract obstruction
Dr. Masami Yamamoto1, Dr. Pedro-José López2
Maternal Fetal Medicine & Paediatric Urology Department
Hospital Padre Hurtado1, Hospital Exequiel Gonzalez Cortes2 &
Clínica Alemana Santiago





Lower urinary tract obstruction (LUTO) is due to posterior urethral valves (PUV) in up to half of the cases, urethral atresia being the second most frequent condition. It occurs more frequently in male fetuses; when it affects females the diagnosis should always be considered doubtful and probably attributed to megacolon, vaginal abnormalities or other differential diagnoses. The disease is relatively infrequent, with a reported incidence of 2 every 10.000 births in England. The main interest of this disease is that antenatal therapy has been developed to shunt the fetal urine to the amniotic cavity, and preserve renal function. Nevertheless, the selection criteria are rigorous and not all males with LUTO are suitable for antenatal intervention.

Diagnosis can be made from the first trimester by ultrasonography, usually performed at 11 to 14 weeks. The bladder is normally visualized in a sagittal view, measuring not more than 1 cm in most cases. When is associated with other abnormalities such as increased nuchal translucency or malformations, the suspicion of an associated aneuploidy is strengthened.

In the second trimester, the bladder is normally bigger in size, with important variation in growing phase and micturition.  Typical characteristics are the size of the bladder and bilateral pyelectasia or even hydronephrosis as LUTO produces retrograde urinary tract dilation. The characteristic sonographic image of the “keyhole sign” is described when the upper urethra and the bladder are dilated. However, this is not a constant finding.

Antenatally LUTO is diagnosed by the detection of a distended bladder that does not empty, unilateral or bilateral upper tract dilatation with or without oligohydramnios. In a male fetus with these findings in isolation it must be assumed to be PUV unless proved otherwise.

Amnio infusion has been used to increase the ultrasound diagnosis. Frequently, oligohydramnios present because of LUTO makes the diagnosis of other abnormalities difficult.

This is routinely recommended in all institutions, as fetal gender can be confirmed and normal karyotype could further select the cases that could benefit from antenatal treatment. This can be performed by amniocentesis.

Natural history and prognosis.
Several studies consistently demonstrate that mortality is high, around 60%. This elevated mortality could rise up to 90% whenever persistent oligohydramnios was associated, with renal morbidity and pulmonary hypoplasia. These cases developed end stage renal dysfunction in 30% of the cases. Other adverse prognostic factors are early gestational age at presentation.

In LUTO, the postnatal renal impairment is important, as antenatal therapy is not indicated in cases in which the function is definitely impaired.  This is not an easy subject as fetal markers of function are in continuous evolution.  Urinary sodium <90mmol/L  is normal at 20 to 30 weeks of gestational age. Whenever this is found >1Also an elevation of urinary B2 Microglobulin >13mg/L has been shown to correlate well with renal impairment, and >6 to be an adverse prognostic factor.  Fetuses in which urinary biochemical analysis shows impaired renal function are not candidates for antenatal therapy1,2.

Fetal blood creatinine is not a good predictor as it is normally increased during pregnancy. Fetal blood sodium concentration is regulated at the placenta is similar to that of the mother.



Antenatal therapy
Serial vesicocentesis, vesicoamniotic shunts and in-utero percutaneous cystoscopy have been proposed as alternative therapies for LUTO in male fetuses, normal kayotype and preserved renal function. Some centers support that oligohydramnios is not a selection criteria, but rather a contraindication, as these cases could have already an impaired renal function. Antenatal therapy should be offered when neonatal viability is low, and therefore delivery is not an option.

Serial vesicocentesis is performed at no less than two week intervals with fine needles >21G, guided by ultrasound in hands of experienced fetal medicine specialists. The aim is to decompress the bladder and preserve urinary function until delivery. The problem of this approach is that several procedures could increase the risk of miscarriage.

Vesicoamniotic shunts are double pig-tailed catheters that can be inserted percutanously, under ultrasound guidance, in which one end is inserted into the bladder and the other left in the amniotic cavity, through the fetal anterior abdominal wall. The procedure aims to leave a continuous drainage of the fetal urine to the amniotic cavity that can preserve renal function. A review of 169 cases3 showed that the overall survival was 47%, in which 40% of survivors had end-stage renal disease.

The procedure had important complications explaining the low survival such as blockage in 25%, displacement in 20%, preterm labour, miscarriage, chorioamnionitis. Displacement can leave a vesico-amniotic fistula than could continue to be therapeutic, but fetal vesico-abdominal fistula can be produced, leading to ascitis ad sequelae4.

Fetal cystocopy is performed percutaneously, under local anesthesia as fetoscopy. The endocope is inserted into the distended bladder, and mechanical or laser ablation of PUV is intended5. The problem is that frequently, the ablation produces either a perineal fistula -that produces bladder drainage but important perineal lesions-  or a urethra stricture, especially if it is done with laser; therefore until the technology improves is still not an option.

Until 2003, after 25 years of history and treated cases, with more than 300 treated fetuses, a review6 demonstrated that there were no randomized studies. Perinatal survival appeared to improve as compared to the non-drainage group (OR 2.5, 95% CI 1-5.9, p<0.03). This was even stronger in cases defined as poor prognosis (OR 8.9, 95% CI 1.2-52.9 p<0.03. )

Lower urinary tract obstruction is variable in severity and sometimes associated with high mortality. Adverse prognostic factors should be better identified to select those cases that will not invariably die and that may benefit from bladder decompression. Randomized trials are needed to support the indication for intervention.  





1. Johnson MP, Corsi P, Bradfield W et al: Sequential urinalysis
improves evaluation of fetal renal function in obstructive uropathy.
Am J Obstet Gynecol 173: 59, 1995
2. Johnson MP, Bukowski TP, Reitleman C, et al: In utero surgical
treatment of fetal obstructive uropathy:A new comprehensive approach
to identify appropriate candidates for vesicoamniotic shunt therapy.
Am J Obstet Gynecol 170: 1770, 1994.
3. Manning FA, Harrison MR, Rodeck C: Catheter shunts for fetal
hydronephrosis and hydrocephalus: Report of the International Fetal
Surgery Regsitry.N Engl J Med 315: 336, 1986.
4. Crombleholme TM, Harrison MR, Golbus MS, et al: Fetal intervention in
obstructive uropathy: prognositic indicators and efficacy of
intervention. Am J Obstet Gynecol 62: 1239, 1990.
5. Quintero RA, Hume R, Smith C, et al: Percutaenous fetal cystoscopy and
endoscopic fulguration of posterior urethral valves. Am J Obstet
Gynecol 172; 206,1995.
6. Freedman AL, Johnson mP, Smith CA, et al: Long term outcome in
chilndren aftere antenatal intervention for obstructive uropathies.
Lancet 345: 374, 1999.


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