What is the residual risk of chromosome abnormalities after a normal cell-free DNA test?

The residual risk of chromosome abnormalities after a normal cell-free DNA (cfDNA) test is approximately 1% to 2%. Although cfDNA testing has high sensitivity and specificity for detecting chromosomal abnormalities such as trisomy 21 (Down syndrome), it is important to recognize that no screening test is infallible. A normal result from cfDNA testing does not completely eliminate the possibility of chromosomal abnormalities.

The 1% to 2% residual risk accounts for the test's performance characteristics, including false negatives that may occur due to factors like insufficient fetal DNA in the maternal bloodstream or limitations in the technology used. Therefore, while a normal cfDNA test significantly reduces the risk, the remaining risk of chromosomal anomalies still warrants further discussion with patients regarding the possibility of follow-up diagnostic testing if clinically indicated or if there are additional risk factors present. This understanding is crucial for providing comprehensive prenatal care and counseling.