Sensitivity of first-trimester ultrasound in the detection of congenital anomalies in twin pregnancies: population study and systematic review

Introduction: The first aim of this study was to ascertain the diagnostic performance of first-trimester ultrasound in detecting congenital anomalies in twins. The secondary aim was to explore the strength of association between different pregnancy characteristics and early detection of structural anomalies in a large unselected population of twin pregnancies. A systematic review of the published literature was also carried out.

Material and methods: Retrospective analysis of prospectively collected data from consecutive twin pregnancies booked for antenatal care between 1996 and 2014. Predictive accuracy of those covariates independently associated with the occurrence of fetal anomalies was assessed with logistic regression analysis and receiver operating characteristics curves.

Results: In all, 1064 twin pregnancies (820 dichorionic and 264 monochorionic) were included in the analysis. Forty-two pregnancies had one or more fetuses with structural abnormalities. Detection of structural abnormalities using ultrasound was possible in the first trimester in 27.3% (95% confidence interval 15.0-42.8) of twin pregnancies. Monochorionicity (odds ratio 2.3, 95% confidence interval 1.1-4.7) and discordance in crown-rump length and nuchal translucency were associated with an increased risk of fetal anomalies. However, their predictive accuracy was only moderate (areas under the curve 0.67, 95% confidence interval 0.6-0.8 and 0.68, 95% confidence interval 0.6-0.8, for crown-rump length and nuchal translucency discrepancy, respectively).

Conclusions: First-trimester detection of structural abnormalities in twin pregnancies is possible in 27.3% (95% confidence interval 15.0-42.8) of cases. The likelihood for first-trimester detection of structural anomalies in twins was maximum for cranial vault, midline brain and abdominal wall defects. Monochorionicity and increasing discrepancy in crown-rump length and nuchal translucency were associated with fetal structural abnormalities, although their predictive performance was only moderately good.