What is low fetal fraction in NIPT?

Fetal fraction is the proportion of the DNA in your blood sample that comes from the placenta rather than from you. If it is too low, the laboratory cannot produce a reliable result and will report a no-call, failed or inconclusive result. The two best-recognised reasons are a higher body mass index and testing early in pregnancy, particularly before 10 weeks. Neither means anything is wrong with your baby. In twin pregnancies, no-call results are more common. Laboratories generally use the lower of the two fetal fractions to decide whether the sample is adequate, which makes an inconclusive result more likely. What usually happens next is a repeat sample at a slightly later gestation, and most women get a valid result second time. Not always, though — and if repeat testing also fails, you should be offered diagnostic testing rather than left without information. One point to raise with your doctor rather than worry about alone: low fetal fraction has been associated with some pregnancy complications, though ACMG notes that definitive rates and any surveillance protocol have not been established. It is a reason for your obstetrician to be aware, not a reason to assume a problem. ACMG recommends that counselling after an inconclusive result should include the offer of diagnostic testing.