Intertwin discordance in umbilical venous volume flow: a reflection of blood volume imbalance in twin-to-twin transfusion syndrome

Objectives To compare umbilical venous volume flow (UVVF) between donor and recipient twins in twin-to-twin transfusion syndrome (TTTS) using an index that is independent of gestational age and to correlate changes in this index with outcome following endoscopic laser surgery. Methods UVVF was calculated in 84 cases of TTTS by multiplying the umbilical vein cross-sectional area at its entry into the fetal abdomen by time averaged blood velocity. All cases were classified according to the Quintero staging system. The ratio between UVVF in recipients and donors (R/D-UVVF) in each pair of twins was calculated before and 48 h after laser treatment, and changes in R/D-UVVF were correlated with pregnancy outcome. Intraobserver and interobserver UVVF measurement reliability was assessed in 19 singletons, and 13 donor and recipient twins before laser treatment using the intraclass correlation coefficient (ICC). Results Twenty-five, 32, 21 and six cases presented as Quintero Stages 1, 2, 3 and 4, respectively, at a median gestational age of 20 (range, 15–26) weeks. Intraobserver and interobserver ICC for UVVF measurement in twins were 0.97 and 0.67, respectively. UVVF was a median of 2.13-fold (range, 0.3–19-fold) higher in recipients than in donors (137 mL/min vs. 64 mL/min, P < 0.001) and increased with gestational age (r = 0.58, P < 0.001 for recipients, r = 0.62, P < 0.001 for donors). From 68 cases in which R/D-UVVF could be measured 48 h following laser surgery, cases with a favorable outcome showed a significant decrease in R/D-UVVF from a median of 1.97 to 1.27 (P < 0.01) and cases with recurrent TTTS (n = 6) did not (decrease in R/D-UVVF from a median of 2.32 to 2.19, P = 0.17). Using a cut-off of < 30% reduction of R/D-UVVF, 66% of the cases with recurrence could be predicted, and the odds ratio for recurrence was 3.13 (95% CI, 0.52–18.29). A significant UVVF imbalance between recipient and donor twins was found in cases with Quintero Stages 1–3 but not in those with Stage 4. Conclusions In TTTS, UVVF is significantly higher in recipients than in their donor cotwins and the R/D-UVVF seems adequately to indicate the flow imbalance between twins, regardless of gestational age. A decrease in R/D-UVVF could be predictive of a favorable evolution following laser treatment. Copyright © 2007 ISUOG. Published by John Wiley & Sons, Ltd.