Antenatal diagnosis of twin-twin transfusion syndrome by Doppler ultrasound.

We evaluated 31 pairs of twins: six with twin-twin transfusion syndrome, four discordant, and 21 concordant twins. The criterion for the retrospective diagnosis of discordancy was a difference in birth weight of 20% of the larger infant's weight. Using pulsed Doppler evaluation of the umbilical artery of each twin, the pulsatility index (PI) was used to evaluate the umbilical arterial waveforms. The differences in the PI from the twin-twin transfusion syndrome cases between 24-31 weeks significantly exceeded those of the cases without this syndrome (P less than .05). Seven cases had inter-twin differences in PI above 0.5, six of which had the twin-twin transfusion syndrome. The difference in PI seemed to predict the risk of twin-twin transfusion syndrome: The difference was high before the appearance of hydrops fetalis in those with this syndrome, whereas the difference in PI from discordant twin cases, except for those with the syndrome, was low.