Non-invasive prenatal test (NIPT)

This recently developed test is performed from a peripheral blood sample of the pregnant woman after the 10th week of pregnancy and involves the non-invasive risk assessment (screening) for common chromosomal aneuploidies (Non Invasive Prenatal Testing-NIPT), using cell-free fetal DNA in maternal blood (plasma). Its accuracy is estimated at ~ 99% for the detection of Down syndrome (trisomy 21) and is relatively less accurate for other common chromosomal aneuploidies (e.g. 13, 18, X and Y).

Couples should be informed about all the available options in prenatal chromosomal testing, including non-invasive prenatal diagnosis (NIPT), which avoids the risk of invasive procedures, making, but:

  • is not a diagnostic test and
  • is currently limited to the risk assessment for only a few common aneuploidies, basically for Down syndrome

Therefore, the choice of performing NIPT should be a conscious choice of the couple, following appropriate genetic counseling, which should also provide information regarding the serious limitations of the test.

In conclusion, the advantages of NIPT, typically performed between the 10th and 20th week of gestation, focus primary on the ability to detect, with a relatively high success rate, embryos harboring classic aneuploidies-trisomies (for chromosomes 21, 18 and 13 and to a lesser extent for the sex chromosomes X and Y), without the (low) risk of pregnancy complications associated with invasive testing.

The indications for non-invasive prenatal diagnosis, now mainly focus on ‘medium’ risk pregnancies, as revealed through previous first trimester ultrasound (NT) combined with biochemical markers and maternal age.

The limitations of NIPT, as currently applied internationally by all laboratories and according to internationally accepted guidelines, include:

  • A small percentage, in total about 1%, for a false positive or false negative result (especially for X and Y
    chromosomes), including analysis failures
  • The application only in pregnancies with an increased a priori risk for aneuploidy,
  • The absolute necessity of confirming positive findings through an invasive procedure in the 2nd trimester of
  • The problems related to its reliable application in twin and multiple pregnancies

Therefore, a negative/normal NIPT result does not ensure the absence of a chromosomal abnormality in the fetus, while a positive result should be confirmed by invasive prenatal diagnosis.

From the above, it is easily understood that the application of NIPT is not recommended for low-risk pregnancies as a first-tier screening test in the population, while it significantly increases the likelihood of detecting common aneuploidies in high-risk pregnancies. Finally, in pregnancies with ultrasonographic findings associated with structural abnormalities in the fetus, invasive prenatal diagnosis, and not NIPT, should be recommended.