Determining the Uncertainty of Fetal Urine Production Rate Estimations

Abstract

The fetal urinary bladder can be observed by ultrasound and the increasing bladder volume during a filling phase is assumed to reveal the urine production. Volumes, estimated at different time points within the filling phase, allow the hourly fetal urine production rate (HFUPR) to be estimated. HFUPR estimations may add to the knowledge of fetal reactions during obstetrical complications. However, it is essential to know the degree of measurement uncertainty. Otherwise, small deviations may be overrated when repeating HFUPR estimations. The purpose of the current paper was to introduce an interactive program for calculation of HFUPR and the related standard deviation (SD). Furthermore the aim was to evaluate factors which may influence the SD of HFUPR estimations. Using the office software Excel, an interactive program was created and the application was illustrated by the filling phases of 16 fetuses. This material also enabled different realistic sets of estimation data to be simulated. Thus, SDs were calculated based on various numbers of documented bladder images and investigation times. When three instead of two bladder images were used for HFUPR estimation, the mean of SD was reduced from 22.4 to 8.1 mL/h (p \ 0.0001). When the time from the first to the last measurement expanded from 10 to 30 min and four bladder images were used, the mean of SD was reduced from 7.5 to 2.4 mL/h. (p \ 0.0001). An interactive program for calculation of HFUPR and the related SD was provided. Reductions in the SD with increasing number of bladder measurements and time span between measurements were demonstrated.