Non-invasive Down Syndrome Test Is Accurate

Exercise and overnight rest may help prenatal screening

/ Author:  / Reviewed by: Robert Carlson, M.D

(RxWiki News) For most women, prenatal screening is important. Prenatal screening enables doctors to detect diseases or conditions in a growing baby before it is born.

One recent international study has good news: a non-invasive genetic test for Down syndrome and Edwards syndrome is more accurate than the current methods for trisomy testing.

"Talk to your doctor about prenatal screening."

A study published in the American Journal of Obstetrics and Gynecology found that a genetic test called Digital Analysis of Selected Regions (DANSR) is almost 100% accurate in predicting Down syndrome, known as trisomy 21, and Edward’s syndrome, known as trisomy 18.

Lead investigator Mary E. Norton, MD director of perinatal research at Lucile Packard Children’s Hospital at Stanford University, and her team looked at 4,002 pregnant women from the U.S., the Netherlands and Sweden. The average age of the women was 34.3 years, and the group was racially diverse.

The doctors examined blood samples taken from the women using DANSR, a method that analyzes small fetal cell-free DNA fragments, and looks at specific chromosomes instead of the whole genome, making it more efficient and less costly. 

This method was combined with Fetal-fraction Optimized Risk of Trisonomy Evaluation (FORTE), a computer algorithm that takes into account a mother’s age and the amount of fetal DNA in the sample, and then scores the likelihood of the baby having a trisonomy disorder.

Norton found that after more than 900 cases were excluded for various reasons, the DANSR and FORTE analysis identified 100% of the 81 cases of Down syndrome.

There was one false positive among the 2,888 normal pregnancies, a a false-positive rate of 0.03 percent. The analysis identified 37 of 38 cases of Edwards syndrome, with two false-positives among the 2,888 normal cases, with a false-positive rate of 0.07 percent.

The finding shows that this test for birth defects is more successful than current screening tests, which confirm the presence of Down syndrome and Edwards syndrome inaccurately 2-3 percent of the time and fail to predict the conditions at least 5 percent of the time.

If a trisomy disorder is detected, it must be confirmed by invasive procedures, such as amniocentesis or chorionic villus sampling, which may cause a woman to miscarry, although the occurrence is rare. However, the accuracy of the new screening procedure means invasive procedures would not be needed.

“Cell-free DNA offers high accuracy with a single blood test,” said Dr. Norton in a press release. “[This method] is potentially suitable as a replacement for current, relatively inefficient aneuploidy screening.”

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Review Date: 
June 5, 2012
Last Updated:
June 8, 2012