Doppler assessment of the uterine circulation in the second trimester in twin pregnancies: Prediction of pre-eclampsia, fetal growth restriction and birth weight discordance

Objective: To compare singleton nomograms of the uterine circulation with previously established twin nomograms in the prediction of pre-eclampsia, fetal growth restriction (FGR), and birth weight discordance ≥ 20% in twin gestations. Methods: This was a retrospective analysis of maternal and perinatal data obtained from 256 dichorionic twin pregnancies. The mean uterine artery resistance index was calculated 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 of either singleton or twin nomograms. Results: According to twin reference values, 14.0% of patients were screen positive, compared to only 3.1% when singleton reference values were used. The sensitivity of abnormal uterine artery Doppler results defined by twin nomograms vs. singleton normograms was 36.4% vs. 18.2% for pre-eclampsia, 26.7% vs. 9.7% for FGR, 28.9% vs. 7.9% for birth weight discordance ≥ 20%, and 26.5% vs. 10.3% for any adverse outcome, respectively. Conclusion: Despite using specially constructed twin normograms, uterine artery Doppler studies in twin gestations had an overall low sensitivity in predicting adverse obstetric outcome. Negative predictive values of uterine Doppler studies in twin gestations are lower compared to those reported in unselected singleton pregnancies, i.e. maternal and fetal complications occur more frequently despite normal uterine artery waveforms. This suggests that there is an additional pathomechanism, causing pre-eclampsia and FGR in twin gestations, that is unrelated to uteroplacental insufficiency.