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Recording available 2/16-5/2
Recording available 2/16-5/2
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Abstract Award
Abstract Award
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Foundation Awardee

Poster Session 3

Category: Fetal Intervention

Poster Session 3

(870) New insights of the Starling law shows that preload determines UA diastolic flow.

Thursday, February 12, 2026
10:30 AM - 12:00 PM  
Objective:
Counterintuitive is the finding that, in monochorionic pregnancies affected by twin-to-twin transfusion syndrome (TTTS), donors with absent end diastolic flow in the umbilical artery (UA) recover following laser ablation of the anastomosis, which theoretically increases the resistance. The hypothesis is that preload determines cardiac output, explained by the Starling law, and therefore, the UA diastolic flow increases with higher venous flow.

Study Design:

TTTS cases treated in Clinica Universidad de los Andes. Retrospective analysis of Doppler findings in cases with umbilical vein flow (UVF) measurement before and after laser therapy for TTTS. Linear correlation was calculated for Donor and Recipient UVF with UA-PI, MCA-PI, MCA-PSV and DV-PI.

Results:

46 cases of TTTS were included. There was an inverse correlation between UVF and UA-PI in donors (R: -0,4763 P< 0.001) and recipients (R: -0,3677 P< 0.05). This was not found with MCA-PI or MCA-PSV. There was an inverse correlation between UVF and DV-PI in donors (R: -0,3072 P< 0.05), but not in recipients.

Following laser, there was no correlation between UA-PI and venous flow, although only 21 cases had measurements. There was a significant venous flow increase in the donors (median 28 to 72ml/min, p=0.023)< ![if !supportAnnotations] >[IJVS1]< ![endif] > , and no change in the recipients (p=0.73).

Of the 15 Stage 3 cases, 8 had donor demise before discharge, and two more after discharge. Of the 7 donors alive at discharge, all recovered diastolic flow and the mean UVF increase was 46ml/min (4 cases available measurements, 31-60ml/min increase).

Conclusion:
There was a correlation between UVF and UA end diastolic flow (UA-PI), supporting that lower preload results in reduced end diastolic flow. In stage 3 donors who survived laser therapy, UVF increased. These findings support the hypothesis that low UVF, rather than placental resistance, is the main determinant of end diastolic flow in TTTS.