If the first trimester scan showed that your fetus has an increased risk of chromosomal abnormalities, this does not mean that your fetus definitely has a chromosomal abnormality. This pamphlet contains information about non-invasive prenatal testing (NIPT), which is an additional test that can help provide a clearer answer.

What is NIPT?

Non-Invasive Prenatal Testing (NIPT) is a new method of screening for the most common chromosomal abnormalities in a fetus.

A blood sample is taken from the pregnant woman to determine whether there is a high probability of Down's syndrome (Trisomy 21), Edward's syndrome (Trisomy 18) or Patau’s syndrome (Trisomy 13) in the fetus. The test can also predict the sex of the fetus to a high degree of certainty.

Small quantities of DNA from the placenta can be found in a woman’s blood (cell-free fetal DNA). The placenta contains cells identical to the cells in the fetus, and therefore reflects the fetal DNA. Based on DNA in the mother’s blood, NIPT can assess whether there is a greater probability of an extra chromosome 21, 18 or 13 in the fetus.

Who will be offered NIPT?

In case of an increased likelihood of Down's syndrome (greater than 1:300) or increased risk of Edward’s or Patau’s syndrome (greater than 1:150) you will be offered further testing in the form of chorionic villus sampling(CVS), amniocentesis, or NIPT.

If the fetus has a very large nuchal fold or a deviating blood sample results, we recommend CVS or amniocentesis. If you do not wish to have either of those tests performed, NIPT can be used as an alternative. NIPT can be carried out after 11 completed weeks of pregnancy.

NIPT results:

• Low probability (most frequent): It is very unlikely that the fetus has Down’s, Edward’s or Patau’s syndrome.
• High probability (rare): The fetus is expected to have Down’s, Edward’s or Patau’s syndrome. If NIPT shows a high probability of chromosomal abnormality, this will need to be confirmed either by CVS or amniocentesis.
• Sex: The sex of the fetus according to the NIPT analysis.
• Uncertain result in approx. 4% of cases: The amount of DNA from the placenta is not high enough in the blood sample to provide an accurate result. In these cases, we will decide whether a new NIPT should be done or whether to recommend CVS or amniocentesis.
• In rare cases changes can occure in other chromosomes than chromosome 21, 18 and 13. In these cases further investigation is offered. 

Results of NIPT

You will be informed of the results via your E-boks or by the staff at the Ultrasound Clinic (section 449) at Hvidovre Hospital. The results will be ready 10 work days after the blood sample has been taken.

Benefits of NIPT

• High sensitivity regarding Down's syndrome (99%), Edward's syndrome (approx. 95% ) and Patau’s syndrome (approx. 90%)
• No increased risk of miscarriage as the test only requires a blood sample from the pregnant woman.

Disadvantages of NIPT compared to CVS or amniocentesis

•  Chromosomal analysis based on CVS or amniocentesis also detects chromosomal abnormalities other than Down's syndrome, Edward's syndrome and Patau’s syndrome. NIPT screens 80-85% of the abnormalities that can be discovered by CVS or amniocentesis.
• Small risk of false-positive results.
• In very rare cases, NIPT results may be normal even if the fetus does have Down’s, Edward’s or Patau’s syndrome. However, the accuracy of the test is usually very, very, high.

How accurate is NIPT?

NIPT has 99% detection rate for Down's syndrome, and slightly lower accuracy detecting Edward’s syndrome (95%) or Patau’s syndrome (90%). If NIPT shows a high probability of Down’s, Edward’s or Patau’s syndrome, we recommend further testing to confirm the results by CVS or amniocentesis.

Approximately 1-2 out of every 10 NIPTs (10-20%) that show a high probability of a chromosomal abnormality will be false positive, meaning that the NIPT predicted trisomy is not the case. In other words, 80-90% of all NIPT results showing a high probability of trisomy in the fetus are true positives.

For NIPT results that show a low probability of trisomy, 1 out of approx. 1,000 pregnancies will have a fetus with trisomy, despite the normal NIPT result (called a false negative).

Further information

You can find more information about NIPT and other pregnancy screenings at hvidovrehospital.dk/ultralyd (in Danish only). You can also watch a video about the various options if the first trimester scan shows an increased risk of trisomy 21, 18 or 13.