In TTTS, blood volume is increased in Recipients (R) and decreased in Donors (D). We evaluated the relation between UA Doppler and Umbilical Vein volume flow (UVVF). Review of Doppler parameters in TTTS. UVVF Z-scores of consecutive cases were correlated with UA PI, in donors and recipients. 66 of 78 had complete Doppler measurements. Median UA PI was higher and UVVF was lower in donors than Recipients. R (1.42 & 1.19 Wilcoxon paired T p<0.001), UVVF Z-scores (0.68 +-0.25 & 1.00+-0.5 Paired student T p<0.001). Greater UVVF was correlated to lower UA PI both in donors and recipients (p<0.01, Pearson R=-0.3). PI in ductus venosus was not correlated UVF in either twin. Demise 2 days post laser occurred in 13 donors and 4 recipients. These events were better predicted by qualitative assessment of umbilical end diastolic flow than by UA PI or UVF. Absent or reversed end diastolic flow had a 3.45 RR (1.4-8.3) of demise. UVVF z-scores is inversely correlated to UA PI, supporting that hypovolemic state is associated with low cardiac output and low end diastolic velocity. UVVF was not predictive of demise, although qualitative abnormalities such as absent or reversed end diastolic flow were. DV was not associated with UVVF changes, even in recipients. This could be further analysed by stages. Supporting information can be found in the online version of this abstract Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.