OC16.04: *Antenatal characteristics of postnatal diagnosed lower urinary tract obstructions

To assess the prevalence, antenatal diagnostic accuracy and prognosis of postnatally confirmed Lower Urinary Tract Obstruction (LUTO) in fetuses presenting with hydronephrosis and/or obstructive uropathy. This multicentre, retrospective study was conducted in the Netherlands between 2013 and 2023, including 437 fetuses with hydronephrosis and/or suspected obstructive uropathy present during the third trimester of pregnancy. Among the 437 fetuses, LUTO was postnatally diagnosed in 40 male cases, resulting in a prevalence of 9%. Neonatal mortality occurred in 5 LUTO cases (13%). A multilevel obstruction of the upper and lower urinary tract was observed in 20% of the LUTO cases. All surviving infants (n = 35) underwent transurethral resection of posterior urethral valves (TUR), with 69% requiring a second TUR operation. Overall, reflux was detected in 63% and abnormal estimated Glomerular Filtration Rate (eGFR) was noted in 26%. Furthermore, 20% underwent unilateral nephrectomy and 3% developed renal failure and necessitated kidney transplantation. Among the postnatally diagnosed LUTO cases, 13% presented antenatally with isolated hydronephrosis (i.e. normal bladder aspect, absence of ureteral dilatation and normal amniotic fluid indexes) and has been predominantly misclassified as upper urinary tract obstruction. Despite this initially reassuring antenatal ultrasound finding, postnatal outcomes revealed that 20% necessitated nephrectomy. This study highlights that a substantial percentage of postnatally diagnosed LUTO cases did not present any of the classical antenatal indicators of LUTO. This emphasises that, despite an initially not-alarming antenatal ultrasound finding, a favourable postnatal outcome cannot be guaranteed. This underscores the pivotal importance of thorough postnatal follow-up, as the diagnosis of LUTO in male fetuses with unilateral hydronephrosis cannot be completely ruled out in the antenatal period.