OBJECTIVES: To examine umbilical venous volume flow (UVF) dynamics by twin status and disease severity in untreated twin-twin transfusion syndrome (TTTS). METHODS: In 70 cases of untreated TTTS, absolute UVF, UVF corrected for estimated fetal weight (UVF/kg), intertwin difference (DeltaUVF/kg) and recipient to donor ratio (R/D-UVF/kg) were calculated. Parameters for UVF were compared with respect to twin status and disease severity (early, Quintero Stages I and II; advanced, Stages III and IV). RESULTS: UVF/kg was higher in recipients than in donors and decreased with advancing stage in both twins (in recipients, 183.9 mL/kg/min vs. 145.6 mL/kg/min, P = 0.043; in donors, 137.5 mL/kg/min vs. 122.5 mL/kg/min, P = 0.033). Linear regression analysis demonstrated that the overall best correlation coefficient for DeltaUVF/kg was obtained for the Doppler pulsatility index of the umbilical artery (t = - 4.536, P <0.001). In advanced stage, absolute and weight-corrected UVF were lower overall, while significant differences in intertwin volume flows persisted. The lowest flows were observed in hydropic recipients (median, 67.0 (range, 55.2-122.0) mL/kg/min vs. 180.8 (range, 59.1-565.4) mL/kg/min; P = 0.001). CONCLUSIONS: In TTTS, UVF is significantly higher in recipients than in donors. With progression to advanced stage UVF/kg decreases in both twins as the magnitude of UVF that can be accommodated by the recipient declines. Further study of these dynamics in combination with cardiac performance parameters is warranted to refine diagnostic and prognostic assessment.
