Ultrasound assessment of venous blood flow before and after laser therapy: approach to understanding the pathophysiology of twin-twin transfusion syndrome.
OBJECTIVE
To estimate direction and volume of blood exchange between the donor twin and recipient twin by ultrasound assessment of blood flow in the umbilical vein before and after selective laser photocoagulation of communicating vessels (SLPCV) for twin-twin transfusion syndrome (TTTS).


METHODS
Forty-one TTTS patients underwent Doppler examination of the umbilical vein before and 24 h after SLPCV. The diameter and mean time-averaged velocity of the umbilical vein were estimated. Total umbilical venous flow (TUVF) was calculated as follows: TUVF (mL/min) = mean time-averaged velocity (cm/s) x mean cross-sectional area (cm2) x 60 (s).


RESULTS
TUVF was significantly higher in the recipient (111.2 mL/min) than in the donor twin (44.8 mL/min) before SLPCV (P < 0.0001). However, TUVF was no different between the recipient and the donor twin after SLPCV (93.1 vs. 70.7 mL/min, recipient and donor twin, respectively, P = 0.11). The donor twin's TUVF increased after surgery (P < 0.0001), while the recipient twin's TUVF decreased (P = 0.041). The median postoperative increase in the donor twin's TUVF of 25.9 mL/min had a corresponding decrease of TUVF in the recipient twin of 18.1 mL/min (P = 0.27).


CONCLUSIONS
Our data suggest that untreated TTTS is characterized by excessive umbilical venous blood flow in the recipient twin relative to the donor twin. Laser surgery results in concordant changes in umbilical venous flow in opposite directions between the donor and recipient twins, eliminating the initial imbalance. Our results lend support to the fundamental hypothesis of unbalanced blood flow exchange (net flow from donor to recipient) between monochorionic twins as the cause for TTTS and that laser surgery eliminates the pathophysiological cause.
Florida Institute for Fetal Diagnosis and Therapy, St Joseph's Women's Hospital, Tampa, FL, USA.
K
K
Ishii
R H
RH
Chmait
J M
JM
Martínez
M
M
Nakata
R A
RA
Quintero
D001783:Blood Flow Velocity; D005260:Female; D005330:Fetofetal Transfusion / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D006801:Humans; D017075:Laser Coagulation; D011184:Postoperative Period; D011247:Pregnancy; D011446:Prospective Studies; D012039:Regional Blood Flow; D018608:Ultrasonography, Doppler; D016216:Ultrasonography, Prenatal / Q000379:methods*; D014471:Umbilical Veins / Q000000981:diagnostic imaging* / Q000503:physiopathology