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Prenatal Genetic Predisposition Test (NIPT/NIPS): Screening from 10 Weeks, Reliability and Procedure

  • Mar 11
  • 3 min read
NIPT

The non-invasive prenatal test is known by two names:


  • NIPT (Non-Invasive Prenatal Testing)

  • NIPS (Non-Invasive Prenatal Screening)


It is a DNA test performed during pregnancy using a simple blood sample from the pregnant woman. It evaluates the risk of certain chromosomal abnormalities in the fetus, particularly trisomy 21, trisomy 18, and trisomy 13.


This screening test is appreciated because it is:

  • early (from the 10th week of amenorrhea, depending on the laboratory),

  • reliable,

  • and above all safe for the baby, unlike invasive procedures.


Important: NIPT/NIPS is a screening test, not a diagnostic test. A high-risk result must always be confirmed with a diagnostic examination recommended by a healthcare professional.


What is prenatal screening for genetic predisposition?


The term “predisposition” is often used, but in this context it mainly refers to screening for aneuploidies (an abnormal number of chromosomes).

NIPT/NIPS estimates the likelihood that the fetus has certain chromosomal abnormalities by analyzing cell-free fetal DNA circulating in the mother’s blood.


How does the NIPT/NIPS test work?


Circulating fetal DNA: the principle


From about the 10th week of pregnancy, fragments of so-called cell-free DNA circulate in the pregnant woman’s bloodstream. These fragments mainly originate from the placenta.


The laboratory analyzes this DNA and measures the relative quantity of fragments from different chromosomes.


What does the laboratory look for?


If the laboratory detects an excess of fragments from a particular chromosome (for

example chromosome 21), this may indicate an increased risk of trisomy.


Time to receive results

Results are generally available within 1 to 2 weeks, depending on the laboratory and the country.


Which conditions can the NIPT test detect?


Main screening targets (the most common trisomies)


NIPT primarily screens for:

  • Trisomy 21 (Down syndrome)

  • Trisomy 18 (Edwards syndrome)

  • Trisomy 13 (Patau syndrome)


Sex chromosomes and the baby’s sex


Depending on the test offered, screening may also include abnormalities of the sex chromosomes (X and Y), such as:

  • Turner syndrome (45,X)

  • Klinefelter syndrome (XXY)


In some cases, the analysis may also reveal the sex of the baby, if the parents wish to know.


For example, dedicated DNA tests can determine the baby’s sex by detecting the Y chromosome in maternal blood, as explained in this guide on the baby gender DNA test


Expanded NIPT and microdeletions: caution required


Some laboratories offer expanded panels (microdeletions or rare anomalies). However, these analyses may be less reliable and more prone to false positives, so they are usually recommended only in specific situations.


How reliable is the NIPT test?


NIPT is considered highly reliable, especially for:

  • Trisomy 21: sensitivity often > 99%

  • Trisomy 18: around 97%

  • Trisomy 13: about 87–95%


Reliable medical information about prenatal screening can also be found through organizations such as the American College of Obstetricians and Gynecologists (ACOG):


Why is it not a diagnostic test?


Even though NIPT is very accurate, it remains a screening test.

  • A negative result indicates a very low risk, but it does not guarantee with absolute certainty that no anomaly is present.

  • A positive result indicates a higher risk and must be confirmed by a diagnostic procedure recommended by a healthcare professional, such as amniocentesis or chorionic villus sampling (CVS).


Possible causes of difficult-to-interpret results


Certain rare situations may influence the interpretation of results, for example:

  • placental mosaicism,

  • a vanishing twin,

  • a recent blood transfusion,

  • certain maternal biological characteristics.


Why choose a non-invasive prenatal test?


Before the introduction of NIPT/NIPS, prenatal screening mainly relied on first-trimester ultrasound and blood tests, with false-positive rates that could reach around 5%.

If suspicion remained, an invasive diagnostic test could be recommended. These procedures are informative but more demanding and carry a small risk.


The arrival of NIPT has significantly reduced the number of unnecessary invasive tests, including procedures such as amniocentesis.

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