NIP test (NIPT)
NIPT is used to detect trisomies, i.e. the triple appearance of a certain chromosome. During a pregnancy there are namely DNA fragments of the baby in the mother’s blood. These DNA fragments come from the different chromosomes. By counting the number of DNA fragments of the baby, it can be detected how many copies of chromosome 21 are present.
Today NIPT is mainly used to detect Down’s syndrome but trisomy 13 and trisomy 18 can also be detected in this way. The sex can also be determined.
During the test sometimes information can also be obtained about parts of other chromosomes, e.g. too many or too few copies. When that may be relevant for your pregnancy, foetus or yourself, the Centre for Medical Genetics (CMG) will also tell you about the abnormalities.
In order to be eligible for reimbursement by the RIZIV [the NIHDI – National Institute for Health and Disability Insurance], the blood sampling for the NIPT can be carried out at the earliest from the twelfth week of pregnancy. Only from this date is in most cases sufficient DNA from the baby present in your blood.
- How reliable is NIPT?
- What are the risks for my baby if I opt for NIPT?
- When is NIPT used?
- When is NIPT not indicated?
- What are the limitations of NIPT?
- What are the possible results of NIPT?
- When does the result of the NIPT become available?
- How much does the NIPT cost?
NIPT has a sensitivity of more than 99%: out of 100 babies with trisomy 21 the test will detect a minimum of 99 and miss a maximum of 1.
In one per cent of cases NIPT gives a false positive result. That means that if 100 women have the test carried out, one woman has an increased risk passed on whereas the baby does not have trisomy 21.
The NIPT is a non-invasive screening test. The blood sampling poses no risks for the pregnancy.
In view of the fact that in one per cent of women the test is false positive, you have one chance in a hundred of undergoing an invasive test, with increased risk for the baby, whereas the baby does not have trisomy 21.
Since 1 July 2017 NIPT has been reimbursed for any pregnant woman covered by Belgian national health insurance, apart from a small non-refundable part. In other words you do not need to have any specific medical reason to have the test carried out.
Nevertheless a NIPT – even if you would not be eligible for reimbursement – is particularly indicated in the following situations:
- You are very worried and want to have as much certainty as possible about the risk of trisomy 21, 18 or 13 in a non-invasive manner.
- You had an earlier pregnancy with trisomy 21, 18 or 13.
- You are 40 years of age or older and therefore are at greatly increased risk of having a baby with trisomy 21, 18 or 13.
- You have another reason. You would do best to discuss this with your doctor: other tests are necessary for certain genetic conditions.
- For patients without Belgian national health insurance: you have a combined test carried out which shows an increased risk of trisomy 21 (> 1/300).
In multiple pregnancies (more than two foetuses). In a twin pregnancy the result is usually very reliable.
When you have had one of the following procedures or treatments in the past three months:
- Blood transfusion
- Stem cell or immunotherapy
- If you have had heparin treatment.
- In the case of some abnormalities in your genetic material or that of your partner (the father of the baby).
In the above situations you can have a combined test carried out.
An invasive test is preferred if ...
- ... abnormalities are found in the baby on the ultrasound (including nuchal fold thickness > 3.5 mm).
- ... you are very obese (with a BMI of 30 and over).
What cannot yet always be detected with NIPT:
- Mosaicism of chromosome 21
- Small abnormalities (deletions or duplications) of chromosome 21
Molecular monogenic abnormalities (among others mucoviscidosis and fragile X syndrome) can also not yet be detected with NIPT.
- The NIPT shows a low risk
No signs have been found of the presence of an extra copy of chromosome 21. Because the NIPT is a screening test (not a diagnostic test) a normal result cannot 100% rule out trisomy 21. Out of 100 babies with trisomy 21 NIPT detects a minimum of 99 and misses a maximum of 1.
- The NIPT shows a high risk
This is a strong indication but does not necessarily mean that the baby has trisomy 21. If the NIPT shows an abnormal number of chromosome 21, this result must be confirmed with an invasive test: a chorionic villus test or amniocentesis. By so doing we examine the inherited material of the baby directly. Only this accompanying diagnostic test can give you full certainty about the question of whether the baby has trisomy 21 or not.
- The NIPT is unclear or unsuccessful
This occurs in three to five per cent of samplings. NIPT is based on a statistical risk calculation. There is the possibility that this calculation is not conclusive and the CMH cannot determine your personal risk of having a baby with trisomy 21. That occurs mainly when there is still insufficient foetal DNA circulating in your blood, e.g. in a blood sample taken before 11 weeks, but also when you are obese. Some treatments, e.g. heparin therapy, can affect the quality of the result.
In the case of an unclear NIPT result, the CMG will carry out a second NIPT free of charge. If this is unsuccessful a second time, you can opt for a combined test. Even if the NIPT is unsuccessful for a technical reason, the CMG will repeat the test on a new blood sample without extra costs.
In prenatal tests the turn-around-time (or TAT) is of course very important. The CMG tries for a TAT for the NIPT of four days, calculated from the receipt of the laboratory request and the sample.
For patients with Belgian national health insurance a NIPT has been reimbursed since 1 July 2017. The patients pay only the non-refundable part [excess] (see RIZIV list). In order to be eligible for reimbursement by the RIZIV, blood sampling for the NIPT can only be carried out at the earliest from the twelfth week of pregnancy. Only from then is in most cases sufficient DNA from the baby present in your blood.
For patients without Belgian national health insurance, a NIPT costs 260 euros.