The non-invasive prenatal test (NIPT) is an accurate genetic screening test for common trisomies, sex chromosome aneuploidies and microdeletions.

NIPT differs from conventional prenatal screening methods in two important ways. First, conventional screening methods which use the concentration of serum proteins in maternal blood and on ultrasound have higher false-positive rates (incorrect “high risk” results in an unaffected pregnancy) and false negatives rates (incorrect “low risk” results in an affected pregnancy) than NIPT. Second, conventional screening methods report an individual risk score for a patient which takes into account ultrasound findings, the results of other screening tests and relevant family history. NIPT relies primarily on the relative concentrations of DNA fragments from different chromosomes in the mother’s blood.

This may apply to a young woman with normal fetal ultrasound, or a woman with a low probability result from conventional first trimester screen.

If the NIPT result is LOW PROBABILITY of trisomy 21

It is highly likely that the result is correct, and that the fetus does not have any of the chromosome abnormalities tested. The chance of the fetus being affected is less than 1 in 20,000.

If the NIPT result is HIGH PROBABILITY of trisomy 21

It is possible but not definite that the result is correct, and that the fetus has a trisomy 21. The chance of the fetus being affected is approximately 20%.


A high probability NIPT result is more likely to be correct than a high probability conventional first trimester screen. Nonetheless, a high probability NIPT result must be confirmed by invasive testing by CVS or amniocentesis before making major medical decisions regarding the pregnancy.

This may apply to a young woman with normal fetal ultrasound, or a woman with a low probability result from conventional first trimester screen.

If the NIPT result is LOW PROBABILITY of trisomy 21

It is highly likely that the result is correct, and that the fetus does not have any of the chromosome abnormalities tested.

The chance of the fetus being affected is less than 1 in 10,000.

If the NIPT result is HIGH PROBABILITY of trisomy 21

It is likely but not definite that the result is correct, and that the fetus has trisomy 21. The probability of the result being correct is approximately 50%.


A high probability NIPT result is more likely to be correct than a high probability conventional first trimester screen. Nonetheless, a high probability NIPT result must be confirmed by invasive testing by CVS or amniocentesis before making major medical decisions.

This may apply to an older woman, or a woman with a high probability result from conventional first trimester screen.

If the NIPT result is LOW PROBABILITY of trisomy 21

It is likely that the result is correct, and that the fetus does not have any of the chromosome disorders tested.  The chance of the fetus being affected is less than 1 in 5,000.

If the NIPT result is HIGH PROBABILITY of trisomy 21

It is highly likely but not definite that the result is correct, and that the fetus has a trisomy 21. The probability of the result being correct is approximately 90%.

In this setting, a high probability NIPT result must be confirmed by invasive testing by CVS or amniocentesis before making major medical decisions.

This may apply to a woman whose fetus has malformations on ultrasound, or who has a very high probability from conventional first trimester screening.

NIPT is a screening test and may be less useful in this setting. It may be more appropriate to bypass NIPT and consider invasive testing by CVS or amniocentesis. .

 

If the NIPT result is LOW PROBABILITY of trisomy 21

A low probability result for trisomy 21 is still likely to be correct, but the possibility of a ‘false negative’ result is increased. The possibility of a false negative result can be exacerbated if the placenta is malfunctioning (which can be a feature of fetal trisomy). It is also possible that the fetus has a chromosomal abnormality that is not tested by NIPT.

Invasive testing by CVS or amniocentesis should be considered despite the low probability result.

 

If the NIPT result is HIGH PROBABILITY of trisomy 21

It is highly likely that the result is correct, and that the fetus has a trisomy 21. The probability of the result being correct is approximately 99%.

High probability results should be confirmed by invasive testing before acting on that result.