Charts of fetal size: kidney and renal pelvis measurements.

OBJECTIVE: To construct new size charts for fetal kidney measurements and to define normal limits for renal pelvic antero-posterior diameter. METHODS: A prospective, cross-sectional study was carried out in the ultrasound department of a large hospital. Six hundred and sixty-three fetuses were scanned only once for the purpose of the study at gestations between 14 and 42 weeks. Centiles for kidney dimensions were estimated by combining separate fractional polynomial regression models fitted to the mean and standard deviation, assuming that the measurements have a normal distribution at each gestational age. Centiles for renal pelvic diameter were obtained using quantile regression. RESULTS: Size charts for fetal kidney dimensions [antero-posterior (AP), transverse, length and volume] and renal pelvis diameter are presented and compared with previously published data. CONCLUSION: We present new size charts for fetal kidney size that take into consideration the increasing variability with gestational age. These data should aid the prenatal diagnosis of renal pathology by defining renal size and the upper limits of normal pelvic dilatation. They may be particularly useful in the third trimester where there is limited data available. Our data confirm that it is reasonable to use an upper limit of 7 mm for the AP diameter in late pregnancy.