Noninvasive prenatal testing (NIPT) is a blood screening test can assess the risk of a fetus will be born with certain genetic abnormalities. The testing analyses small amounts of fetal cell free DNA that is in the mother’s bloodstream. The source of this cell free fetal DNA is the placenta and in most cases is identical to the DNA of the fetus.
NIPT is most commonly used to look for chromosomal disorders that are caused by the presence of an extra or missing chromosome (aneuploidy).
Down Syndrome (Trisomy 21) – extra chromosome 21
Turner’s (monosomy X) – a missing X chromosome
Klinefelter’s – and extra X chromosome
NIPT can also screen for additional disorders that are caused by missing (deleted) or copied (duplicated) sections of a chromosome.
The fetal fraction must be above 4% to give a reliable result. Common reasons for a low fetal fraction include doing the test too early, maternal obesity or fetal aneuploidy.
Because NIPT analyses both fetal and maternal cell free DNA, the test can sometimes detect a genetic condition in the mother.
It is important to remember that NIPT is a screening test that can determine whether the fetus is at higher or lower risk for a condition but there can still be false positive and negative results with the screening. If a patient has a positive test, counseling to discuss the results and the options for additional testing including invasive diagnostic testing is advised.