Prenatal genetic tests allow us to identify mutations in DNA or abnormalities in fetal chromosomes in a targeted way. In the laboratory these analyses have a higher priority than postnatal tests due to their preventative nature. That is because if there is a severe abnormality the patient may decide to terminate the pregnancy or choose extra monitoring during pregnancy and after birth.
For monitoring purposes usually we carry out a test on the pregnant woman's blood sample and/or (possibly) a sample of her partner.
Due to time pressure, prenatal molecular and biochemical screening are greatly targeted.
What does the non-invasive prenatal test do?
NIPT is used to detect trisomy, i.e. a particular chromosome that occurs three times. During pregnancy, fragments of the baby's DNA circulate in the mother's blood stream. These DNA fragments are derived from the different chromosomes. By measuring the number of these DNA fragments, the number of copies of chromosome 21, 18 and 13 can be determined, and so the presence of trisomy 21, 18 or 13 can be predicted.
NIPT is used chiefly to detect Down syndrome nowadays, but it can also detect trisomy 13 and trisomy 18. The test may also detect information about parts of other chromosomes, e.g. too many or too few copies. If this information is relevant for your pregnancy we also report on these abnormalities.
The blood test will only be reimbursed by the Belgian national health security system (RIZIV/INAMI) from 12 weeks of gestation onwards, because this is when enough DNA of the baby can be found in your blood.
- More than 30,000 tests for trisomy 21, 13 and 18 have currently already been successfully completed, with an unheard of sensitivity of almost 100% in pregnant women with a proven risk.
- The risk for a false negative test result is very low: less than one percent. In other words, out of 100 babies with trisomy 21 the test will detect a minimum of 99 and miss maximum 1.
- In one percent the NIPT gives a false positive: when 100 women have this test,one woman will be told there is an increased risk of trisomy 21, whereas the baby does not have trisomy 21.
- NIPT is a non-invasive screening test. The blood test holds no risk for the pregnancy.
- As the test can show a false positive in one percent of women, this means that you have one chance out of a hundred of having an invasive test, with an increased risk for the baby, whereas it does not have trisomy 21.
As announced by Minister De Block NIPT will be reimbursed for every pregnant woman from 01-07-2017 onwards.
Until 30-06-2017 NIPT still needs to be paid completely or partially (depending on your social security) by the patient. Currently NIPT can be considered in the following situations:
- you had a combined test which shows an increased trisomy 21 risk (> 1/300),
- you had a previous pregnancy with trisomy 21,
- you are 40 or older and therefore you have a strongly increased risk of a baby with trisomy 21,
- you are very concerned and you want as much certainty as possible about trisomy 21 in a non-invasive way,
- another reason. It is best to discuss these with your doctor because certain genetic disorders require other tests.
NIPT is not recommended:
- in case of a multiple pregnancies, except twin pregnancies
- if you (the mother) had a blood transfusion, a transplant, stem cell or immunotherapy over the past three months, or an ongoing heparin therapy
- in case of abnormalities in your genetic material or in the father’s.
An invasive test is recommended
- if the ultrasound shows abnormalities in the baby (including nuchal thickness > 3.5 mm),
- if you (the mother) suffer from serious obesity (with BMI of 30 and more).
NIPT determines the number of 21, 13 and 18 chromosomes, and can detect the sex.
The following disorders cannot always be detected with NIPT:
- mosaicism of chromosome 21, and
- small abnormalities (deletions or duplications) of chromosome 21.
Molecular monogenic abnormalities (such as cystic fibrosis and fragile X) cannot be detected with NIPT yet.
- The NIPT shows a low risk.
No indications have been found for the presence of an extra copy of chromosome 21. NIPT is a screening test (not a diagnostic test): a normal result cannot exclude trisomy 21 for 100%. Out of 100 babies with trisomy 21, NIPT detects a minimum of 99 and misses maximum one.
- NIPT shows a high risk.
This is a strong indication, but does not necessarily mean the baby has trisomy 21. When NIPT shows an abnormal number of chromosome 21, the result needs to be confirmed by an invasive test: chorionic villus sampling or an amniocentesis.
This additional diagnostic test provides direct information about the fetus' genetic material, which is the only way to say with certainty whether the baby has trisomy 21.
- The NIPT is unclear or unsuccessful. This occurs in three to five percent of tests.
NIPT is based on statistical risk calculations. These may not be conclusive, which means the test cannot determine your personal risk of a baby with trisomy 21. This is mainly due to insufficient foetal DNA circulating in your blood. This is for instance possible if the blood test is taken before 11 weeks, but also if you are obese. Some therapies, e.g. heparin therapy, can influence the quality of the test.
- In case of an unclear NIPT the test is repeated on a new blood sample without extra costs. Only after a second failed NIPT we can opt for a combined test. If there are technical reasons for the failure, NIPT is repeated on a new blood sample without extra costs.
- In rare cases
- NIPT can detect other chromosome abnormalities in the fetus, e.g. trisomy 18 or 13, or a clinically relevant chromosome abnormality in you (the mother).
In these cases the CMG will notify you or your gynaecologist.
- ...we find indications for another problem or illness in you, e.g. a chromosome abnormality or a type of cancer. Naturally, further examinations must confirm the suspected abnormality or illness.
We anticipate a short turn around time (TAT).
Until further notice of official bodies we will keep the same TAT. The result is usually known after two weeks (maximum three weeks). We aim as soon as possible at a 4-day TAT, starting from the day of receipt of the lab request and blood sample.
This test is currently not or partially reimbursed by your health insurance and costs EUR 290 since December 1st 2016.
As announced by Minister De Block, the NIPT will be reimbursed for every Belgian pregnant woman from 1st of July 2017 onwards. The NIPT will then cost 260 euro, of which a maximum of 8,68 euro will be charged to the patient.