Ultrasound measurement of fetal urine flow.

In summary, the measurement of fetal urinary flow remains controversial because the actual volumes of the human fetal bladder are unknown. The volume formula for an ovoid overpredicts fetal bladder volume and has a wide margin of certainty. The best ultrasonographic prediction of bladder volumes were calculated by applying a regression formula to the area of a sagittal sonographic image of the bladder (0.46323 + 1.39394.sagittal area). Calculations of the HFUFR based on the ovoid volume formula may be overestimated by 40%-70%. However, HFUFR estimated by regression of three to six longitudinal bladder area measurements is better with a narrow margin of uncertainty (+/- 35%). This technique affords improved accuracy and is easier and more convenient.