Three‐dimensional sonographic assessment of fetal urine production before and after laser surgery in twin‐to‐twin transfusion syndrome

Abstract

Fetal urine production in twin-to-twin transfusion syndrome (TTTS) reflects the hemodynamic imbalance between the donor and recipient twins but it has not been measured in this particular condition. The aim of this study was to measure fetal urine production using three-dimensional (3D) ultrasound in donor and recipient twins before and after laser treatment for TTTS and to correlate this with umbilical venous volume flow (UVVF). Urine production rate (UPR) was measured using 3D ultrasound with Virtual Organ Computer-aided AnaLysis (VOCAL) in 106 cases of severe TTTS. The rotation angle was set at 30 degrees . The bladder volume was measured twice in each fetus (V(1) and V(2)), with an interval of 5-30 min between measurements, in order to calculate the UPR. When V(2) > V(1), UPR was calculated using the formula: V(2) - V(1) /time interval. Together with UPR, UVVF was measured before and after treatment. Both parameters were corrected for fetal weight. Inter- and intraobserver variability were calculated in 16 cases using the intraclass correlation coefficient. Before laser treatment, UPR was significantly higher in recipients compared with donors (median, 14.8 and 0 mL/h/kg, mean 23.8 and 2.3 mL/h/kg, respectively, P < 0.001), and UPR was positively correlated with UVVF in both twins. Following laser treatment (48 h later), UPR decreased to 9 mL/h/kg (P < 0.001) in recipients, while there was no change in donors. UVVF increased significantly from a median value of 92 to 132 mL/min/kg (P < 0.01) in donors and decreased significantly from 150 to 99 mL/min/kg (P < 0.001) in recipients. In TTTS UPR is correlated to UVVF and reflects the hemodynamic imbalance between donor and recipient twins. Following laser treatment, UPR decreases in recipients but is unaffected in donors. However, changes in UVVF occur in both twins. This suggests that although fetal renal function is driven by fetal hemodynamics, there may be a lag in the recovery of renal function in the donor twin.