cfDNA Testing Accurately Detects Fetal Trisomies in Twin Pregnancies

Harmony used Digital ANalysis of Selected Regions (DANSR) assays, which targeted sequences on chromosomes 13, 18 and 21 for chromosome quantitation and single‐nucleotide polymorphisms on chromosomes 1–12 for fetal‐fraction measurement. Products of the DANSR assays were quantified using either next‐generation sequencing or a custom microarray; both were used during the course of this study.

Results showed that the cfDNA test correctly classified 16 (94.1%) of the 17 cases of trisomy 21, nine (90.0%) of the 10 cases of trisomy 18, one (50.0%) of the two cases of trisomy 13 and 962 (99.4%) of the 968 cases without any of the three trisomies.

In addition to the fresh cfDNA test results, the investigators conducted a literature search that identified seven relevant studies, excluding their own previous papers because their data were included in the current study. Combining the populations of this study and the seven studies identified by the literature search, analysis revealed 56 trisomy‐21 and 3718 non‐trisomy‐21 twin pregnancies. The pooled weighted detection rate (DR) and false‐positive rate (FPR) were 98.2% and 0.05%, respectively.

The authors concluded that while cfDNA testing is not now recommended for use in twin pregnancies, these latest findings provide compelling evidence that mothers carrying twins should not be denied this safe and effective test.

The study was published in the June 4, 2019, online edition of the journal Ultrasound in Obstetrics & Gynecology.

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