The significance of non-visualization of the fetal bladder during an ultrasound examination to evaluate second-trimester oligohydramnios.

Our objective was to determine the pregnancy outcome after targeted sonography performed for the evaluation of second-trimester oligohydramnios fails to visualize the fetal bladder. A retrospective review identified patients in 1990-94 who were referred for targeted sonography from 16 to 24 weeks to evaluate oligohydramnios. The ultrasound records and photographs from the initial examination were reviewed and compared to later pregnancy outcome data obtained by reviewing delivery and neonatal records, neonatal renal ultrasound reports or autopsy information. Complete outcome data were available in 98 patients. The fetal bladder was not visualized in 29 patients (30%). Post-delivery analysis of the fetal urinary tract was performed in 25 patients either by autopsy or by neonatal renal ultrasound scanning. A severe anatomic malformation of the urinary system was present and had been detected by targeted sonography in 23 of 25 cases (92%). The remaining two fetuses were found to have anatomically normal urinary tracts at autopsy, but other pathological findings suggested that a functional derangement of the urinary system had led to non-visualization of the bladder at ultrasound examination. Non-visualization of the fetal bladder during targeted sonography to evaluate oligohydramnios indicates a severe anatomic or functional problem of the fetal urinary tract. In our study, this ultrasound finding was associated with universal fetal or neonatal death.