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

Background

Ultrasonographic features of the underlying hemodynamic changes in twin-twin transfusion syndrome (TTTS) may be present at the first trimester scan.

Aims

To investigate the value of intertwin discordance in nuchal translucency (NT) thickness and crown rump length (CRL) to predict TTTS and other adverse outcomes.

Study design

Cohort study.

Subjects

One hundred and thirty-five unselected consecutive monochorionic diamniotic twin pregnancies.

Outcome measures

NT 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.

Results

TTTS 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).

Conclusion

In 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.