Cell-Free DNA Screening During Pregnancy

To the Editor In the JAMA Insights Clinical Update on noninvasive prenatal screening using cfDNA, the authors discussed test failures that occur when the fraction of fetal DNA is too low, leading to a diagnostic test. The cited fetal fraction threshold of 4% is historical and modeled and follows empirical reasoning. However, a standard method for its calculation has not been set, and higher levels of detection for common aneuploidies at fetal fractions between 2% and 4% can be obtained using proprietary algorithms.