Three-dimensional indices of renal perfusion in normal pregnancy and pre-eclampsia

We compared renal perfusion in normal pregnant women and women with pre-eclampsia using three-dimensional (3D) ultrasound. We measured the flow index (FI), vascular index (VI) and vascularisation flow index (VFI) which are believed to reflect vascularity and flow intensity.

Fourteen patients with normal pregnancy and 16 patients with pre-eclampsia were recruited. Imaging was conducted using a Voluson E8 machine and a 6-MHz trans-abdominal probe. The inferior border of the maternal left kidney was scanned. Volumes were acquired using 3D power Doppler angiography (3D-PDA). The FI, VI and VFI were generated using 'histogram' facility.

Maternal characteristics between normal pregnant women and women with pre-eclampsia were not different in terms of maternal age, gestation or body mass index. Depth of insonnation was not different between groups. The FI, VI and the VFI were not different between groups. The mean (SD) for FI was 27.9 (7.4) vs. 27.1 (6.5) between women with normal pregnancy vs. women with pre-eclampsia. For VI, mean (SD) was 72.3(31.6) vs. 79.4 (28.7) respectively. For VFI, mean (SD) was 20.8 (10.8) vs. 20.8 (8.1) respectively. Using the Mann-Whitney U test, no statistical differences between groups were apparent. There was no correlation between FI measurements and maternal creatinine (Pearson's R square = 0.04; p = 0.45) or with maternal urea levels (Pearson's R square = 0.20; p = 0.10).

Using 3D ultrasound, we failed to demonstrate a difference in maternal renal perfusion in normal pregnancy compared to pre-eclampsia. The lack of observed difference may be a reflection of the high variability in 3D measurements (i.e. poor investigative tool) rather than a true lack of difference in renal perfusion.