A test that assesses "cell-free" fetal DNA in pregnant women's blood significantly improves detection of Down syndrome and other chromosomal disorders compared with traditional blood testing, according to a new study in The New England Journal of Medicine. The findings could change how low-risk women are screened for fetal genetic problems and could reduce the number of women who undergo invasive procedures such as amniocentesis -- which pose risk of miscarriage -- to confirm a diagnosis. Researchers performed cell-free DNA testing on blood samples of 1,914 pregnant women who were undergoing standard fetal chromosomal screening at 21 centers across the U.S. False positive rates with cfDNA testing were well under the rates for standard screening -- 0.3% vs. 3.6% for trisomy 21 (Down syndrome) and 0.2% vs. 0.6% for trisomy 18. The two methods detected all cases of trisomies 21, 18 and 13, for an overall negative predictive value of 100%. Positive predictive values for cfDNA testing compared with standard tests were 40.0% and 8.3% for trisomy 18 and 45.5% and 4.2% for trisomy 21. Read the abstract.