Discordance in crown‐rump length and nuchal translucency thickness in the prediction of adverse outcomes among monochorionic diamniotic twin pregnancies: A single‐center retrospective cohort study from Vietnam

Abstract Objective To evaluate the usefulness of first‐trimester crown‐rump length (CRL) and nuchal translucency (NT) thickness discordance in predicting adverse outcomes in monochorionic diamniotic (MCDA) twin pregnancies. Methods This retrospective cohort study enrolled MCDA twin pregnancies in which CRL and NT were measured at 11–13 +6 weeks of pregnancy and collected for pregnancy outcomes between January 2022 and June 2023 at Tu Du Hospital in Vietnam. The intertwin discrepancy of CRL and NT was calculated as a percentage of the larger fetuses and smaller fetuses. Regression analysis was used to determine the significance of the association between the intertwin discordance in NT and CRL and the development of twin‐to‐twin transfusion syndrome (TTTS), fetal growth restriction (FGR), intrauterine fetal demise (IUFD), and those with normal outcomes. Receiver operating characteristic curves were constructed to evaluate the performance of inter‐twin discrepancy in the prediction of FGR, TTTS, and IUFD. Results A total of 294 MCDA twin pregnancies were studied. Among them, 149 cases (50.7%) had at least one adverse outcome. The complications included TTTS in 82 cases (55.0%), FGR in 89 cases (59.7%), one IUFD in 95 cases (63.8%), and two IUFDs in 19 cases (12.8%). CRL discordance greater than 10.0% and NT discordance greater than 20.0% were not related to TTTS and IUFD, only to FGR. A CRL discordance greater than 20.0% decreased the survival rate of fetuses. CRL discordance greater than 10.0% had specificity in diagnosing TTTS, IUFD, and FGR of more than 80%, whereas, NT discordance greater than 20.0% had specificity in detecting these complications of more than 50.0%. A predictive model including CRL and NT discordance showed a poor value with area under the curve of:0.69 (95% confidence interval 0.69–0.75). Conclusion In MCDA twin pregnancies, discordant CRL greater than 10.0% was related to FGR. Meanwhile, an intertwin discordance of NT thickness greater than 20.0% was not related to TTTS, FGR, and IUFD. However, adequate surveillance is still required.