Theoretical kidney volume versus real kidney volume: comparative evaluation in fetuses

In order to present equations and normal growth curves of the theoretical kidney volume we studied 290 kidneys taken from 145 fresh human fetuses ranging in age from 13 to 36 weeks post-conception (WPC). The kidneys were evaluated in terms of greatest longitudinal length (L) superior pole width (SW), inferior pole width (IW), thickness (T) and real volume (RV). The theoretical kidney volume was calculated (ellipsoid formula: volume = length x width x thickness x 0.5236) by using SW, IW and the arithmetic mean between SW and IW. The assessment of the theoretical volume by using IW was well correlated with the real kidney volume. We found no statistically significant difference between right and left kidneys. During the second trimester (13 to 24 WPC) there was no difference in kidney volume between male and female fetuses. In the third trimester (25 to 36 WPC) male fetuses presented kidney volumes significantly greater than female fetuses. To evaluate the theoretical kidney volume in fetuses, one may use the IW, which is a quickly and easily obtained measurement. During the second trimester one may monitor the fetal kidney using equations and growth curves without taking the fetal sex into account. During the third trimester the fetal kidney volume must be evaluated using specific curves for male and female fetuses.