OBJECTIVE: This study was undertaken to measure fetal renal volume by means of three-dimensional ultrasonography and to use those data to establish the accurate constant and formula for fetal renal volume assessment with two-dimensional ultrasonography. STUDY DESIGN: Singleton fetuses between 15 and 40 weeks' gestation were included. The volumes of both fetal kidneys were measured with three-dimensional ultrasonography. Three fetal renal diameters (largest anteroposterior, transverse, and longitudinal diameters) were measured, and the constant of the fetal renal volume formula was calculated. Linear regression curves were made for each kidney from the fetal renal volume, the three diameters, and the constant. RESULTS: A total of 112 fetuses were included. The following fetal renal volume formula was established: Fetal renal volume = Constant (R) x Largest anteroposterior diameter (x) x Largest transverse diameter (y) x Largest longitudinal diameter (z). The volumes, the three diameters, and the constants appeared different between the right and left kidneys but not statistically significantly so. CONCLUSION: Three-dimensional ultrasonography is useful in assessing fetal renal volume. The fetal renal volume formula makes possible accurate measurements of fetal renal volume by two-dimensional ultrasonography.
