Ultrasound prediction of intertwin birth weight discordance in monochorionic diamniotic twin pregnancies

OBJECTIVES: To estimate the accuracy of ultrasound to predict birth weight (BW) and BW discordance in monochorionic diamniotic (MCDA) twin pregnancies.

METHODS: A prospective series of MCDA twin pregnancies was subjected to ultrasound fetal weight estimations (EFW) at 16, 20, and 26 weeks of gestation and within 2 weeks of birth. Intertwin weight discordance (DeltaEFW and DeltaBW) was calculated. The correlation between DeltaEFW, DeltaBW, EFW, and BW was assessed (Pearson) and least square regression analysis was performed. Positive and negative predictive values of ultrasound to detect severe DeltaBW were calculated. Receiver-operating characteristics (ROC) curves were constructed to predict DeltaBW >25% at different time points of gestation.

RESULTS: Sixty pregnancies were included. Median DeltaBW was 9.98%. Ten(16,7%), 8(13,3%) and 5(8,3%) twin pairs had a DeltaBW >20%, >25% and >30%, respectively. BW and EFW (r = 0.96; p < 0.001) as well as DeltaBW and DeltaEFW were well correlated with each other (r = 0.75; p < 0.001). Bland-Altman analysis showed that ultrasound evaluation overestimated DeltaBW if >20%. Negative predictive value of ultrasound for DeltaBW >25% was 98%. The area under the curve (AUC) to predict a DeltaBW >25% at 16, 20, and 26 weeks and <2 weeks before birth was 0.79, 0.87, 0.93, and 0.95, respectively.

CONCLUSIONS: Ultrasound estimations of BW and DeltaBW are highly correlated with actual BW and DeltaBW in MCDA twin pregnancies.