SMFM Consult: Ultrasound in the cfDNA era
Q: Should cfDNA screening be offered to women when structural fetal anomalies are detected?
The presence of fetal structural abnormalities significantly increases the risk that a fetal chromosomal abnormality or a copy number variant detectable by microarray is present. While those aneuploidies detectable by cfDNA screening make up a significant proportion of such abnormalities, many structurally abnormal fetuses have chromosomal abnormalities that are not detectable by cfDNA screening.
Women who decline diagnostic testing may request cfDNA screening as an alternative. If this approach is chosen, they should be counseled that there is a substantial risk that a chromosomal abnormality other than trisomy 21, 18, and 13 is present and will not be detected by cfDNA screening.
While some expanded cfDNA screening panels have been reported to detect a select few targeted microdeletions, and one panel offers evaluation of all chromosomes at a resolution of 7 megabases (similar to that of conventional karyotype), the detection and false-positive rates of such panels have not been studied in prospective clinical trials. In addition, such panels are able to detect only a very small percentage of the total number of copy number variants that can be identified with chromosomal microarray.
Pregnancy management should not be altered solely based on the results of cfDNA screening, as false-positive and false-negative results are possible. For women who decline diagnostic testing in the setting of fetal structural abnormalities, pregnancy management should depend on the entire clinical scenario including the specific abnormalities present, gestational age, and preferences of the woman, as well as the results of the cfDNA screen.