ABSTRACT
The most common cause of lower urinary tract obstruction (LUTO) is posterior urethral valves. This occurs in male fetuses (in female fetuses, it is usually part of a cloacal anomaly). The most important factor in the morbidity and mortality from fetal urethral obstruction is pulmonary hypoplasia secondary to oligohydramnios.76
For patients with posterior urethral valves, prenatal diagnosis defines a subgroup of patients with very poor prognosis, with 64% incidence of renal failure and transient pulmonary failure, compared to 33% in the postnatally diagnosed group.77 Serial fetal urine analysis may provide prognostic information in this group of fetuses. Drainage of the bladder three times at 48-72hour intervals with measurement of sodium, chloride, osmolality, calcium, β-2 microglobulin, and total protein should be performed to determine renal function. A decrease in the electrolytes, proteins, and tonicity correlate with a favorable outcome.78
