Fetal DNA a complementary Down’s test

A prospective UK study of 1000 women involved screening for trisomies 21, 18 and 13 using cell-free DNA testing at 10 weeks, followed by combined ultrasound and biochemical screening at 12 weeks.

The false positive rate was 0.1% for cell-free DNA testing and 3.4% for the combined test, while both tests detected all trisomies.

However, in 5% of cases, the first blood test for cell-free DNA failed to determine a result, and 4% of women who had cell-free DNA testing had a missed miscarriage