A previously healthy multigravida was admitted to hospital at 36 weeks' gestation with nausea, vomiting, and diarrhea. Vital signs were normal as were her laboratory data except for moderate ketonuria. A fetal nonstress test was negative, but a sonogram showed severe oligohydramnios. With the presumptive diagnosis of acute gastroenteritis, IV hydration was initiated with lactated Ringer's solution. Despite infusion of 4,000 ml, the patient remained oliguric. Specific gravity of her urine was 1.030. A CVP line was inserted measuring 0 cm. An additional 2,500 ml of crystalloid fluid brought CVP up to 5–6 cm; urine output increased while its specific gravity decreased to 1.001. Repeat sonographic examination 10 hours after maternal urine output had reached 100 ml/h showed adequate amniotic fluid. The mother recovered and delivered a healthy baby 1 week later; the amount of amniotic fluid at delivery was normal.