To develop Z-scores reference ranges for kidney in normal fetuses from the measurements of gestational age (GA), biparietal diameter (BPD) or femur length (FL) using two-dimension ultrasound.

A retrospective cross-sectional study of 403 singleton normal fetuses was performed. The gestation age range was from 18 to 40 weeks. Fetal biologic parameters included GA and BPD and FL based on menstrual age. Left kidney length and left kidney width of normal fetus were measured. Normal Z-score ranges were developed for left kidney length or left kidney width using GA, BPD and FL as independent variables.

Linear regression model was the best description of the data in each case and correlation between left kidney length or left kidney width and independent variables were excellent (r=0.8761, 0.8818, 0.8797, 0.8604, 0.8723, 0.8643). All P values were less than 0.01. The equations were as follows, Y=0.094 22+ 0.1088X, Y=0.132 57+ 0.4349X, Y=0.6664+ 0.491 05X, Y=0.060 58X-0.051 98, Y=0.262 19X-0.197 55, Y=0.294 02X+ 0.136 19. Heteroscedasticity of standard deviation (s) with increasing independent variables also could be modeled with a simple linear (r=0.925, 0.934, 0.915, 0.908, 0.914, 0.922), All P values were less than 0.01. The equations were as follows, Y=0.025+ 0.005 58X, Y=0.097 09+ 0.010 45X, Y=0.046 17+ 0.025 65X, Y=0.001 13+ 0.002 24X, Y=0.003 67+ 0.011 55X, Y=0.005 07+ 0.015 89X. Then we got Z-scores based on the equation, Z-score= (actual measurement data of left kidney length or left kidney width-predictive data of left kidney length or left kidney width) predictive s.

Normal reference ranges and Z-scores for fetal left kidney length and left kidney width had been provided. These normative data may be useful tools for assessment of fetal kidney length and kidney width, especially had potential applications in malformations of fetal kidney.