Importance: With advances in prenatal cell-free DNA (cfDNA) technology, the information available with cfDNA continues to expand beyond the common fetal aneuploidies such as trisomies 21, 18, and 13. Due to the admixture of maternal and fetal/placental DNA, prenatal cfDNA remains a screening test with the possibility of false-positive and false-negative results.
Objective: This review aims to summarize unusual incidental maternal and fetal genomic abnormalities detectable by cfDNA and to provide anticipatory guidance regarding management.
Evidence acquisition: Of 140 articles identified with keywords such as "incidental" and "discordant" cfDNA, 55 original research articles, review articles, case series, and societal guidelines were reviewed.
Results: Prenatal cfDNA may incidentally identify a spectrum of maternal genomic abnormalities such as malignancy, mosaicism, and copy number variants. When discordant with fetal diagnosis, these cases require additional investigation with maternal genetic testing and follow-up evaluation. Such incidental fetal/placental abnormalities may include rare autosomal trisomies, uniparental disomy, and triploidy. Further evaluation of fetal/placental abnormalities can be pursued with a combination of ultrasound and prenatal diagnosis with chorionic villous sampling and/or amniocentesis. Societal guidelines do not currently recommend cfDNA screening for rare autosomal trisomies, microdeletions, or copy number variants, and some experts suggest that sex chromosome screening should be opted in after counseling.
Conclusions: Knowledge about possible incidental findings with prenatal cfDNA is needed to inform pretest and posttest counseling with appropriate follow-up evaluation.
Relevance: As cfDNA technology has advanced to include genome-wide findings, it is important for clinicians, genetic counselors, and societal guidelines to acknowledge the spectrum of possible results outside of the traditional and sex chromosome aneuploidies.