A new study, published online in the American Journal of Obstetrics and Gynecology states that false positive and false negative results have been produced by current Down syndrome and Edwards syndrome screening methods, but researchers have found a new genetic test which is close to 100% accurate.
The research shows that Down syndrome, caused by fetal trisomy 21 (T21) and Edwards syndrome, caused by fetal trisomy 18 (T18) have false negative rates of 5% or higher, and false positive rates from 2-3%.
When a screening result comes back as positive, it is necessary to confirm the positive result by using chorionic villus or amniocentesis sampling, which results in 1 fetal death per every 300 procedures.
To find the new method, researchers used Digital Analysis of Selected Regions (DANSR), which examines fetal cell-free DNA, the small DNA parts which in pregnant mothers, circulates in the bloodstream.
The study states that this test is different than others because DANSR solely examines the chromosomes which need to be looked at. Therefore, the course of action is quicker and not as expensive as other methods.
To determine the results, a breakthrough technique is used, called the Fetal-fraction Optimized Risk of Trisomy Evaluation (FORTE). The FORTE looks at percentages of fetal DNA present in the sample and risks related to age in order to find out whether there is a risk of trisomy in the baby.
4,002 pregnant women with an average age of 34.3 years, with a range of different ethnicities and races, from Sweden, the Netherlands, and the U.S were part of the NICE (Non-Invasive Chromosomal Evaluation).
Before undergoing any testing to determine if there was a risk of trisomy, the women had their blood taken, which resulted in 774 samples being taken out of the trial before continuing. Of the remaining 3,228 samples, 91 were discarded because they failed to meet testing standards. In addition, 57 were counted out because the fetal cfDNA was low.
The High Risk and Low Risk analyses, determined by using the DANSR and FORTE were compared with outcomes from CVS and amniocentesis.
Of the 81 T21 cases that were determined as High Risk, the DANSR and FORTE method identified 100% of them, and only had one false positive when it came to the 2,888 normal results. This gave the DANSR and FORTE method a false-positive rate of only 0.03%.
In addition, out of 38 T18 cases, 37 which were determined as High Risk by the method and 2 false positives were detected. This means the method had a success rate of 97.4% and a false positive rate of only 0.07%
Mary E. Norton, MD, director of perinatal research at Lucile Packard Children’s Hospital at Stanford University commented:
“The improvement in sequencing efficiency achieved by the DANSR platform provides a more affordable, scalable approach to cfDNA analysis with high throughput and potential for widespread clinical utility. Cell-free DNA offers high accuracy with a single blood test. It is potentially suitable as a replacement for current, relatively inefficient aneuploidy screening.”