Prospective Validation of First-Trimester Ultrasound Characteristics as Predictive Tools for Twin-Twin Transfusion Syndrome and Selective Intrauterine Growth Restriction in Monochorionic Diamniotic Twin Pregnancies

Abstract

Objective: Monochorionic diamniotic (MCDA) twins are at increased risk of adverse outcome due to unequal placental sharing and placental vascular communications between the fetal circulations. Most centres perform ultrasound examination every 2–3 weeks to identify these complications. Identifying a high-risk cohort of MCDA twins in the first trimester would allow more efficient surveillance. We have attempted to validate first-trimester ultrasound characteristics as predictive tools for twin-twin transfusion syndrome (TTTS) and selective intrauterine growth restriction (sIUGR) in MCDA twins. Material and Methods: This is a prospective cohort study including MCDA twins enrolled at the time of first-trimester combined screening. Differences in crown-rump length (CRL), nuchal translucency (NT) thickness, ductus venosus pulsatility index for veins (DV PIV), presence or absence of tricuspid regurgitation and right ventricular E/A ratio were assessed. Receiver operating characteristic (ROC) curves were used to assess the potential value of these measures as predictive tools for identifying a cohort of MCDA pregnancies at high risk of adverse pregnancy outcome. Results: Sixty-five MCDA pregnancies were included in the analysis. Nine (14%) developed TTTS, 17 (26%) developed sIUGR. The best predictive marker for TTTS was NT discordance of ≥20% (ROC AUC = 0.79; 95% CI 0.59–0.99). Combining measures did not improve performance (AUC = 0.80; 95% CI 0.62–0.99). Conclusion: NT discordance was the most effective characteristic at predicting TTTS but still had a relatively poor positive predictive value (36%). Intertwin differences in CRL, DV PIV and E/A ratio were not predictive of subsequent pregnancy complications. None of these characteristics have sufficient efficacy to be used to triage MCDA twin pregnancies ongoing obstetric surveillance.