Objective:

Review how the biology of cell-free fetal DNA (cffDNA) may limit noninvasive prenatal testing (NIPT) and identify research directions that could improve it.

Approach:

• Review focus: The review examines cffDNA’s origins, structure, and transport in maternal blood, and considers how these features affect NIPT.
• Research priorities: The authors call for studies to establish cffDNA’s cellular origin and determine how much circulating DNA is associated with extracellular particles.

Key Findings:

• cffDNA is a small fraction of circulating DNA, is difficult to distinguish from maternal DNA, and may not always represent the fetal genotype.
• Much of the DNA called “fetal” originates from the placenta; placental mosaicism can make its genotype differ from the fetus.
• Circulating cffDNA includes fragments of varied sizes and forms, including circular DNA, ultrashort fragments, and fragments longer than 500 base pairs.
• The mechanism by which cffDNA circulates remains unresolved; direct evidence for release in apoptotic extracellular vesicles is lacking.
• The article reports that 47% of high-risk NIPT results are false alarms and require confirmation through invasive diagnostic testing.

Interpretation:

The authors suggest that better understanding of cffDNA biology could enable fetal-DNA enrichment using features such as fragment size, density, molecular associations, or placental surface markers. They note that the biology must be better defined before NIPT can reliably progress from screening to comprehensive genetic diagnosis.

Limitations:

• The review describes unresolved questions about cffDNA’s cellular origin, circulation, and relationship to fetal genotype.
• The context does not provide details of the review’s methods or evidence-selection process.

Conclusion:

The authors identify immunoaffinity enrichment and microfluidics, alongside sequencing and bioinformatics advances, as potential approaches for improving NIPT after the underlying biology is clarified.

Sources:

• Article context; review published in Science Advances