Cell-free fetal DNA (cfDNA) / Non-Invasive Prenatal Testing (NIPT) is used for aneuploidy screening. The fraction of cell-free DNA in maternal plasma that is of placental (fetal) origin is called the fetal fraction. Below what fetal fraction is NIPT considered a 'no-call' result requiring repeat testing or invasive confirmation?
- A <2%
- B <4% ✓
- C <8%
- D <10%
Correct answer: B. <4%
Explanation
A fetal fraction below 4% of total cfDNA is the standard threshold below which NIPT results are unreliable and reported as a 'no-call' (failed result). Low fetal fraction is more common with obesity (dilution effect), early gestational age, and fetal aneuploidy (particularly trisomy 18 and triploidy). When a no-call result is reported, the options are repeat cfDNA testing (if gestational age permits) or offer of invasive diagnostic testing. Fetal fraction typically ranges 10–20% between 10–20 weeks.
Reference: Williams Obstetrics, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.