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Fetal Diagn Ther. 2014;35(3):204-11. doi: 10.1159/000356495. Epub 2013 Nov 15.

Cell-free DNA analysis for trisomy risk assessment in first-trimester twin pregnancies.

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Harris Birthright Research Centre of Fetal Medicine, King's College Hospital, London, UK.



To examine the clinical implementation of chromosome-selective sequencing of cell-free DNA (cfDNA) in maternal blood and an algorithm that relies on the lower fetal fraction contribution of the 2 fetuses in the assessment of risk for trisomies in twin pregnancies.


Risk for trisomies 21, 18 and 13 by cfDNA testing were estimated in stored plasma samples obtained at 11-13 weeks' gestation from 207 pregnancies with known outcome and prospectively in 68 twin pregnancies undergoing screening at 10-13 weeks.


Risk scores for trisomies were provided for 192 (92.8%) of stored plasma and for 63 (92.6%) of the prospective cases. In the retrospective study, 10 of 11 trisomic pregnancies were correctly identified with no false positive results. In the prospective study, 3 trisomic pregnancies were correctly identified with no false positive results. The median of the lower fetal fraction in the prospective study of twins was 7.4% (IQR range 5.9-10.0%), which was lower than in our previous study in singletons (median 10.0%, IQR 7.8-13.0%).


cfDNA testing in twins is feasible but the reporting rate of results is lower than in singletons due to a lower fetal fraction.

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