Amboss writes, that if screening results are abnormal, invasive prenatal diagnostic testing (CVS, amniocentesis) should be offered. However, "Cell-free fetal DNA may also be performed if the patient desires to avoid invasive testing, but it is also a screening test, which may delay eventual diagnostic evaluation."
ACOG guidelines write, "Confirmatory testing with CVS or amniocentesis is recommended both to confirm the diagnosis and to determine if the aneuploidy is a trisomy or secondary to a translocation....The use of cell-free DNA screening as follow-up for patients with a screen positive serum analyte screening test result is an option for patients who want to avoid a diagnostic test." DOI: 10.1097/AOG.0000000000004084
Source: AMBOSS - https://next.amboss.com/us/article/RN0lag?q=cell%20free%20dna#Y6ecc4d049349fdf5f7cd62013a24ba5a
