Discordance in twins: Association versus prediction.

Weight discordance is among the major determinants of perinatal outcome in twin pregnancies. Weight discordance can occur in each trimester of pregnancy, though the clinical meaning of such finding and the association with adverse perinatal outcome can vary according to the gestational age (GA) at detection of growth discrepancy. Discrepancy in fetal size in the first trimester of pregnancy is associated with an increased risk of anomalies, aneuploidy, and fetal loss, though the predictive accuracy of using discordance to predict perinatal outcome is low. Conversely, discordance in the third trimester of pregnancy can be associated with fetal growth restriction, perinatal mortality, and morbidity. In view of these associations, twin pregnancies should be monitored for the occurrence of growth discrepancy. The present review aims to provide an up-to-date critical appraisal of the diagnosis and clinical management of twin pregnancies complicated by growth discordance according to the trimester at presentation.