Nuchal translucency thickness and crown rump length discordance for the prediction of outcome in monochorionic diamniotic pregnancies

BackgroundUltrasonographic features of the underlying hemodynamic changes in twin–twin transfusion syndrome (TTTS) may be present at the first trimester scan.AimsTo investigate the value of intertwin discordance in nuchal translucency (NT) thickness and crown rump length (CRL) to predict TTTS and other adverse outcomes.Study designCohort study.SubjectsOne hundred and thirty-five unselected consecutive monochorionic diamniotic twin pregnancies.Outcome measuresNT and CRL discordance were assessed at 11 to 13+ 6 weeks' gestation. Receiver–operating characteristics (ROC) curves were used to determine their predictive ability for the subsequent development of TTTS.ResultsTTTS complicated 16/135 (12%) pregnancies. Four other pregnancies were complicated by selective intrauterine growth restriction (sIUGR) and 3 by miscarriage < 24 weeks gestation. The median NT discordance was 15% (range 0–37%) in TTTS pregnancies, 13% (12–19%) in those with miscarriage < 24 weeks’ gestation, 47% (30–50%) in those with sIUGR, and 14% (0–86%) in those without complications. Prediction for subsequent development of TTTS provided by the discordance in CRL, expressed as the area under ROC curve, was 0.52 (95% confidence interval 0.38–0.67), while it was 0.50 for NT discordance (95% confidence interval 0.35–0.64). NT discordance was significantly higher in sIUGR compared to both uncomplicated and TTTS pregnancies (p = 0.004 and p = 0.003, respectively).ConclusionIn an unselected population of monochorionic twin pregnancies, discordance in CRL and NT measured during first trimester scan is not a clinically useful predictor of the subsequent development of TTTS. Therefore, strict ultrasound follow up is recommended for the timely diagnosis of TTTS.