Functional evaluation of normal kidney by three‐dimensional (3D) ultrasonography – the hourly fetal urine production rate

Abstract

Background and objective: Fetal urine is the main source of amniotic fluid, which is very important marker of fetal wellbeing. Single deepest pocket measurement or amniotic fluid index method are widely used to evaluate amniotic fluid volume. They are well correlated with real amniotic fluid volume in cases of normal amniotic fluid volume. However, they are not in extreme cases, which are clinically more important. Direct measurement of fetal urine production may be another option to evaluate amniotic fluid volume and fetal kidney function. Moreover, it is well known that 3D USG is superior to 2D USG especially in volume measurement of irregular shape object. We undertook this study to measure the hourly fetal urine production rate (HFUPR) with 3D US in normal pregnancies and evaluate its clinical implication and feasibility.Material and methods: From 20 weeks of gestation to term, 157 pregnant women were enrolled. We used Voluson 730 to measure 3D bladder volume. Vocal (virtual organ computer aided analysis) software was used to measure the volume. Initially, we measured the volume of fetal urinary bladder and observed whether the bladder was emptying or not in 5 and 10 min after initial measurement. We excluded 35 cases whose bladder was found empty within 5 min. If distended bladder was still found, we calculate the HFUPR. We constructed a best‐fit graph of the HFUPR according to gestational age (GA) in weeks.Results: We constructed the following quadratic equation and plotted a graph on the basis of our data. We also showed 10 and 90% values of each gestational week.Conclusion: We demonstrated that serial 3D USG assessment of fetal bladder volume could be used as an alternative method to evaluate amniotic fluid volume.