Normal range for fetal urine production rate by 3-D ultrasound in Brazilian population

The aim of the present study was to establish the normal range for fetal UPR in the Brazilian population.

A cross-sectional study was performed in 167 normal singleton fetuses with gestational ages ranging from 20 to 40 weeks. UPR was measured using 3-D US virtual organ computer-aided analysis (VOCAL). UPR (in ml/h) was calculated during the filling phase by using the equation UPR = (VFB(2) - VFB(1))/time. The values for UPR were plotted as a function of gestational age to obtain a nomogram. Interobserver reliability was also investigated by using Spearman's rank correlation for comparison of paired samples in cases of replication between observers. Bland and Altman's graphical approach was utilized to investigate the agreement between observers.

A total of 167 normal singleton fetuses with gestational age between 20 and 40 weeks were investigated. Nine 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 gestational age generated a curve that represents the normal range for fetal UPR in the Brazilian population, and is expressed by the equation: Ln (UPR) = -13.7508 + 0.7094 × GA - 0.0092 × GA(2) (R (2) 0.60). A correlation coefficient of 0.9994 (Spearman) was obtained. Bland and Altman's graphic plots confirm the significant agreement between observers.

Small differences were observed between the values for UPR observed in our sample and the normal values described in previous studies. These differences were observed mainly in late third trimester and are probably related to population biometric differences.