The role of ultrasound in the prediction of birth weight discordance in twin pregnancies: are we there yet?

Abstract

To analyze the accuracy of ultrasound prediction of birth weight discordance (BWD) and the influence of chorionicity and fetal growth restriction (FGR) on ultrasound performance. Retrospective analysis of 176 twin pregnancies at a Portuguese tertiary center, between 2008 and 2014. Last ultrasound biometry was recorded. Cases with delivery before 24 weeks, fetal malformations, interval between last ultrasound and deliver >3 weeks, twin-to-twin transfusion syndrome and monoamniotic pregnancies were excluded. The accuracy of prediction of BWD was assessed using the area under the receiver-operating characteristics curve (AUC). BWD ≥20% was present in 21.6% of twin pregnancies. EBW had the best predictive performance for BWD (AUC 0.838, 95%CI 0.760-0.916), with a negative predictive value of 86.9% and a positive predictive value of 51.3%. Chorionicity did not influence ultrasound performance. None of the biometric variables analyzed was predictive of BWD in pregnancies without FGR. The accuracy of ultrasound in the prediction of BWD is limited, particularly in pregnancies without fetal growth restriction. Clinical decisions should not rely on BWD alone.