Evidence Library · Other screening

The older screening tests, and why they are still around

Combined screening and the quad screen.

Before cfDNA, screening for Down syndrome used a nuchal translucency measurement on ultrasound plus blood markers in the first trimester, or a blood test alone in the second. These are still used, sometimes because of cost or insurance.

In the FASTER trial of 38,167 women, at a fixed 5% false-positive rate, detection of Down syndrome was 87% for first-trimester combined screening at 11 weeks, 85% at 12 weeks, 82% at 13 weeks, and 81% for the second-trimester quad screen. Combining first and second-trimester information raised detection to 95% or 96%.

Note the fixed 5% false-positive rate. That means about 1 in 20 women screened were told they had a positive result. In the NEXT trial the false-positive rate for standard screening was 5.4% against 0.06% for cfDNA.

Where this comes from:

146. Norton ME, Jacobsson B, Swamy GK, Laurent LC, Ranzini AC, Brar H, et al. Cell-free DNA analysis for noninvasive examination of trisomy. N Engl J Med. 2015;372(17):1589-1597.

151. Malone FD, Canick JA, Ball RH, Nyberg DA, Comstock CH, Bukowski R, et al. First-trimester or second-trimester screening, or both, for Down's syndrome. N Engl J Med. 2005;353(19):2001-2011.

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