First‐trimester ultrasound markers for prediction of adverse outcome in monochorionic diamniotic twin pregnancy

Objective: To investigate the role of intertwin discordance in crown–rump length (ΔCRL) and nuchal translucency thickness (ΔNT) in predicting twin-to-twin transfusion syndrome (TTTS), selective intrauterine growth restriction (sIUGR) and composite adverse outcome in unselected monochorionic diamniotic (MCDA) twin pregnancy. Methods: MCDA pregnancies that underwent first-trimester screening ultrasound between January 2014 and January 2023 at the twin clinic in the Department of Obstetrics and Gynecology, ASST Spedali Civili of Brescia, Italy, were identified retrospectively from our fetal ultrasound database. From medical records, we extracted information on adverse outcome, defined as the development of TTTS, sIUGR or composite adverse outcome (one or more of: fetal loss, need for fetoscopic laser surgery, preterm delivery before 32 weeks of gestation, low birth weight (< 3rd percentile) and neonatal death). We compared the incidence of adverse outcomes between the group with and that without intertwin ΔCRL ≥ 10% and between the group with and that without intertwin ΔNT ≥ 20%. The ability of ΔCRL and ΔNT to predict pregnancy complications was examined using the area under the receiver-operating-characteristics curve (AUC). Results: The study included 177 unselected MCDA twin pregnancies. Of these, 20.9% developed sIUGR, 15.8% developed TTTS and 36.2% had the composite adverse outcome. Furthermore, 36.7% had ΔNT ≥ 20% and 11.3% had ΔCRL ≥ 10%. Compared to pregnancies with ΔNT < 20%, those with ΔNT ≥ 20% had a significantly higher incidence of TTTS (9.8% vs 26.2%; P = 0.004) and composite adverse outcome (30.4% vs 46.2%; P = 0.035), but there was no difference in their incidence of sIUGR (17.9% vs 26.2%; P = 0.191). The AUC for the performance of ΔNT in the prediction of TTTS was 0.647 (95% CI, 0.530–0.763) and that for composite adverse outcome was 0.595 (95% CI, 0.510–0.681). Compared to MCDA pregnancies with ΔCRL < 10%, those with ΔCRL ≥ 10% demonstrated a significantly higher incidence of sIUGR (17.2% vs 50.0%; P = 0.001), but there was no difference in their incidence of TTTS (15.9% vs 15.0%; P = 0.915) or composite adverse outcome (35.0% vs 45.0%; P = 0.382). The AUC for the performance of ΔCRL in the prediction of sIUGR was 0.595 (95% CI, 0.479–0.710). Conclusion: In MCDA pregnancies, ΔNT ≥ 20% is associated with increased risk of TTTS and composite adverse outcome, and ΔCRL ≥ 10% is associated with increased risk of sIUGR. However, their predictive value is too low to warrant changes in clinical practice. © 2025 International Society of Ultrasound in Obstetrics and Gynecology.