OBJECTIVE: The aim of this study was to assess hourly fetal urine production rates (HFUPRs) and establish a nomogram by measuring bladder volumes with 3-dimensional ultrasound. STUDY DESIGN: Fetal urine bladder volume was estimated in 167 normal singleton pregnancies with neither oligohydramnios nor polyhydramnios, at a gestational age of 20-41 weeks. HFUPR was estimated in a regression analysis that included at least 3 volumes calculated during the filling phase with the Virtual Organ Computed-aided AnaLysis (VOCAL) technique. We estimated interoperator variability for HFUPR less than 10 mL/h and HFUPR greater than 10 mL/h. RESULTS: Fetal urine production rates at 25, 30, 35, and 40 weeks were 7.5, 22.2, 56.1, and 125.1 mL/h, respectively. The intraclass correlation coefficients for interoperator variability were 99.2% for HFUPR less than 10 mL/hour and 97.1% for HFUPR greater than 10 mL/h. CONCLUSION: Prenatal measurement of HFUPR with 3-dimensional VOCAL ultrasound is reproducible and may help to determine the cause and prognosis of amniotic fluid volume abnormalities.