Acute oligohydramnios: antenatal expression of VURD syndrome?

Oligohydramnios (OA) is nowadays regarded as one of the best markers of renal function (RF) impairment in bladder outlet obstruction (BOO) detected in utero. As such, its onset is usually early and progressive because of decline in fetal urine production. A series of acute OA complicating pregnancies with BOO has never been reported.

Over a 7-year period, 5 fetuses with in utero suspicion of BOO exhibited an abrupt decrease of amniotic fluid after the 30th week of gestation.

All fetuses were delivered by cesarean section: diagnosis was posterior urethral valves in 3 cases, urethral atresia in 1, and prune-belly syndrome in 1. Urologic work-up demonstrated a unilateral vesicoureteral reflux dysplasia (VURD syndrome) in all 5 fetuses. RF at 1 year was normal in 4 fetuses and impaired in 1.

Besides obstetrical reasons, OA may also have acute onset occurring in the presence of anomalies of the urinary tract; although diagnosis is almost always BOO, functional and anatomical characteristics of the urinary tract are those of VURD syndrome with a non-functioning, refluxing renal unit. The associated acute OA/VURD syndrome may represent a milder expression of a pop-off mechanism advocated in this syndrome with a more favorable prognosis than progressive OA detected early in pregnancy.