Noninvasive Prenatal Screening Test Validated for Trisomies

Diagnosis of fetal aneuploidies relies on invasive testing by chorionic villous sampling (CVS) or amniocentesis in pregnancies that are identified by screening to be at high-risk for such aneuploidies.

A recently developed cell-free DNA (cfDNA) test which uses the Ion Proton sequencing platform and an algorithm that determines the relative number of chromosomal copies enabling detection of fetal trisomies has been assessed.

Scientists at King's College Hospital (London, UK) carried out a nested case-control study of stored maternal plasma from 242 singleton pregnancies at 11 to13 weeks’ gestation, including 201 with euploid fetuses, 35 with Down's syndrome (trisomy 21), 4 with Edwards' syndrome (trisomy 18), and 2 with Patau's syndrome (trisomy 13). A non-invasive prenatal screening test (NIPT) was used to analyze the blood samples.

The samples were analyzed with the IONA test and IONA Software (Premaitha Health plc; Manchester, UK). All 242 samples were processed with the IONA test that measures the relative amount of chromosomes 21, 18, and 13 in the maternal plasma sample to calculate a likelihood ratio to predict the presence of a trisomy. This data is coupled with the background risk associated with maternal age to determine an adjusted probability of the fetus having a trisomy of chromosome 21, 18, or 13.

Of the 242 samples; 35 were trisomy 21, 4 were trisomy 18, and 2 were trisomy 13, and therefore the IONA test detected 100% of all trisomies. This nested case-control study has demonstrated that in pregnancies considered by the combined test to be at high-risk for trisomies 21, 18, or 13, cfDNA testing of maternal plasma at 11 to 13 weeks’ gestation by the IONA test and IONA software, correctly identified all trisomic pregnancies with no false positives.

William Denman, MD, chief medical officer at Premaitha, said, “These results confirm what our customers have already reported; that the IONA test is a highly accurate, robust and simple screen for Down's syndrome and other serious genetic conditions. It is a great endorsement of the test that a scientific team has chosen to verify it. We believe this should encourage broader and appropriate uptake of NIPT, benefiting pregnant women and their families through the increased accuracy, especially the reduction in false positive results that the IONA test provides.” The study was published online on September 21, 2015, in the Journal of Ultrasound in Obstetrics and Gynaecology.

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