Doppler assessment of the uterine circulation in the second trimester in twin pregnancies: prediction of hypertensive disorders, small‐for‐gestational age and weight discordance

Objective:  To compare singleton nomograms of the uterine circulation with previously established twin nomograms in the prediction of hypertensive disorders, small-for-gestational age (SGA) and birth weight discordance >20%. Methods:  This was an analysis of maternal and perinatal data obtained from 256 diamniotic–dichorionic twin pregnancies. The uterine artery resistance and pulsatility index were calculated as a mean from both sides and the presence and absence of notching was recorded. Cut-off levels for abnormal flow parameters were the 95th centile of reference ranges using singleton and twin nomograms. Results:  As mean uterine artery indices are lower in twin gestation, a higher number of patients (n = 73; 28.5%) was screen positive according to twin reference values when compared to those of singletons (n = 51; 19.9%). However, singleton reference ranges or recording of notches only proved to be more efficient than twin reference ranges to correctly predict SGA (17.6, 19, 13.7%), birth weight discordance >20% (30.6, 37.5, 23.9%), and hypertensive disorders (23.5, 21.4, 16.4%), respectively. Compared to singleton nomograms of uterine artery Doppler, twin nomograms had higher sensitivities, lower specific and positive predictive values, but equal negative predictive value to comprise adverse pregnancy outcomes. Conclusion:  For routine clinical practice, it seems justified to use singleton nomograms to assess uterine circulation in twin gestation. However, as the negative predictive value of uterine Doppler studies is slightly lower when compared to singletons, maternal and fetal complications might occur despite normal uterine waveforms.