Screening for trisomies 21, 18 and 13 by cell‐free <scp>DNA</scp> analysis of maternal blood at 10–11 weeks' gestation and the combined test at 11–13 weeks

The performance of first-trimester cfDNA testing for trisomies 21 and 18 in the general population is similar to that in high-risk pregnancies. Most false-positive and false-negative results from cfDNA testing could be avoided if the a priori risk from the combined test is taken into account in the interpretation of individual risk.