Invasive testing for fetal aneuploidies with chorionic villus sampling can be minimized by analyzing fetal DNA from the mother’s blood during the first trimester, according to two U.K. studies in Ultrasound in Obstetrics and Gynecology.

The first study, involving some 90,000 singleton pregnancies, examined which women should undergo maternal blood cell-free DNA (cfDNA) testing to detect trisomy 21, in addition to ultrasound and biochemical screening. Researchers found that by offering cfDNA testing to women with high-risk biochemical test results, a 98% detection rate could be achieved, with an invasive testing rate below 1%.

The other study used cfDNA testing routinely in 1000 singleton pregnancies, in addition to ultrasound and biochemical studies, to screen for trisomies 21, 18, and 13. All trisomies were detected; the false-positive rate for cfDNA was 0.1%, while ultrasound and biochemical screens had a 3.4% false-positivity.

The authors emphasize that the potential for false-positives dictates the need for invasive testing following abnormal results.

Source: Ultrasound in Obstetrics and Gynecology