Low amniotic fluid secondary to LUTO is first detected at around 16 weeks of gestation when urine becomes the major source of amniotic fluid.
Variables most predictive of LUTO: increased bladder thickness, bladder dilation, oligohydramnios, bilateral ureteral dilation, male sex, and referral before 28 weeks.
Normal amniotic fluid levels in between 20-24 weeks: they will do okay for the first 2 years but 1/3 will develop ESRD. The majority with normal AF at 24 weeks do well without intervention.
Options for prenatal intervention:
- Vesicoamniotic shunt: PLUTO trial intended to enroll 150 patients and only enrolled 30 patients. Intention to treat analysis did not show increased survival. The renal function was low regardless. Complications were common. A meta-analysis of 112 fetuses demonstrated no increased survival at 6,12 or 24 months and no differences in postnatal renal function with the shunt. Both studies did show an increase in perinatal survival, which is the only proven benefit of intervention.
- Fetal cystoscopy: not better or worse than VAS.
Interventions based on severity
- Mild LUTO: no oligo, no cysts, or dysplasia. No intervention
- Moderate LUTO: oligo after 18 weeks without signs of renal cysts or renal dysplasia. Intervention indicated.
- Severe LUTO: anhydramnios or severe oligo with hyperechoic kidneys with cysts and dysplasia. Intervention might prevent pulmonary hypoplasia but renal damage is irreversible. Little chance for intervention to change things.