Normal range for fetal urine production rate customized by biometry.

Objective: The aim of this study was to develop a nomogram for fetal urine production (UPR) using biometric parameters.
Methods: A cross-sectional study was performed in 110 normal singleton fetuses with gestational ages ranging from 20 to 40 weeks. UPR was measured using tridimensional ultrasound (3-DUS) virtual organ computer-aided analysis. UPR (ml/h) was calculated during the filling phase using the equation, UPR = (VFB2-VFB1)/time. The values for UPR were plotted as a function of fetal biometry (femur, humerus, abdominal circumference, and head circumference and biparietal diameter) to obtain a nomogram for each parameter.
Results: A total of 110 normal singleton fetuses with gestational age between 20 and 40 weeks were investigated. Five of them were excluded because the image quality was insufficient for correct visualization of the bladder contour. Linear regression analysis of UPR as a function of femur, humerus, abdominal circumference, and head circumference and biparietal diameter generated curves that represents the normal range for UPR by fetal biometry, and expressed by the following equations: (1) Humerus length (HL): ln (UPR) = -5.9546 + 0.0958 × HL (mm); (R(2) 0.6422); (2) abdominal circumference: ln (UPR) = -1.0981 + 0.158 × AC (mm); (R(2) 0.6328); (3) femur length: ln (UPR) = -1.5133 + 0.0803 × FL (mm); (R(2) 0.6611); (4) biparietal diameter ln (UPR) = -7.8779 + 0.2368 × BPD-0.0012 × DBP(2); (R(2) 0.7066). Although BPD has the highest correlation coefficient (R(2) 0.7066) there was no statistical significant difference between the parameters investigated for UPR prediction.
Conclusion: The use of biometric parameters for prediction of fetal UPR seems to be useful and can avoid the necessity of building local nomograms for different populations. The same strategy should be considered to other fields in fetal medicine.