A new test analyzes the free DNA inside the blood of pregnant women to detect Down Syndrome in fetuses with a greater accuracy than standard tests. The test can be made by women between 10 and 14 weeks pregnant.

Image: Med Guidance

The test was developed by a team at University of California, San Francisco and works by reading free floating DNA in cell-free blood. Samples from nearly 16,000 women were taken and researchers found the DNA test identified all 38 fetuses with Down syndrome in the group. In contrast, the standard test currently in use for Down Syndrome found only 30 of the 38 cases of Down syndrome. It also returned less false positives. The standard test registered  854 false positive results, compared to nine false positive with the cell-free DNA tool.

In the standard test blood is similarly drawn from the pregnant women, only this time it consists of looking for signature hormones and proteins associated with chromosomal defects, in combination with an ultrasound scan that checks for excess fluid in the back of the fetus’s neck, in an area called the nuchal fold. The test proved effective in identifying other less common chromosomal abnormalities as well.

“Among 10 cases of trisomy 18, also known as Edwards syndrome, the cell-free DNA technique pinpointed nine and flagged one false positive,” said the study led by Mary Norton, professor of clinical obstetrics and gynecology at the University of California, San Francisco. “With standard screening, eight were identified and there were 49 false positives,” she added.

You win some, you lose some. The cell-free DNA test didn’t wasn’t able to screen for a range of abnormalities that can show up in standard testing.

“Those women who do opt for cell-free DNA testing should be informed that it is highly accurate for Down syndrome, but it focuses on a small number of chromosomal abnormalities and does not provide the comprehensive assessment available with other approaches,” said Norton for Discovery News.