FETAL DNA TEST
Over the last several years, prenatal screening tests have evolved considerably. There has been a great shift in paradigm, particularly in the new generation of non-invasive tests that detect fetal DNA that normally circulates freely in maternal blood. With the development of technologies such as “next generation sequencing” (NGS), it is now possible to detect the vast majority of the most common types of aneuploidy, such as trisomy 21 (Down syndrome), 18 (Edwards syndrome), and 13 (Patau syndrome), via a simple maternal blood test.
After the tenth week of pregnancy, this type of “non-invasive prenatal test” (NIPT) can detect fetal DNA circulating in maternal blood. It is able to detect 99.9% of cases of trisomy 21, ≥98% of cases of trisomy 18 and 13, with a rate of false positives of only 0.1%. Because there is a certain variation in the quality of different types of NIPT that are available, patients should be cautious in deciding which test to use. We believe that we have selected the NIPT that appears the most effective, using the most up to date scientific techniques.
It is offered at Fertilys with a medical requisition.
Where does NIPT fit within a prenatal screening program?
“Conventional” first trimester prenatal screening, which is done between 11 and 14 weeks of pregnancy, remains the first line recommendation for testing. It combines ultrasound features of the fetus (nuchal translucency, nasal bone, blood flow in the ductus venosus, and cardiac tricuspid valve) with a blood test that checks for placental proteins circulating in maternal blood (beta-hCG and PAPP-A).
Conventional first trimester prenatal screening detects 96% of cases of trisomy 21, and 98% of cases of trisomy 18 and 13, with a rate of false positives of 2.5%. As well as detecting aneuploidy, conventional first trimester prenatal screening allows for the early detection of structural fetal anomalies and the prediction of adverse pregnancy events such as preeclampsia, intrauterine growth restriction, and preterm labour, which is currently not detectable with NIPT.
What then, is the role of NIPT in the framework of a prenatal screening program? At the moment we recommend, as does the Fetal Medicine Foundation in the United Kingdom, to offer NIPT as a contingency test in the first trimester of pregnancy for the following patients:
- Those with an intermediate risk of trisomy (between 1:100 and 1:1000) after conventional prenatal screening, and who remain concerned about the possibility of trisomy.
- Those with a high risk of trisomy (≥1:100), who decline invasive prenatal diagnostic testing such as amniocentesis or chorionic villus sampling, given the risk of fetal loss of 1% that can result from the test. It is important to note that NIPT cannot detect all types of chromosomal anomalies, and that a genetic consultation is recommended.
- Those who remain concerned about the risk of aneuploidy, even after a low risk of trisomy (<1:1000) after conventional prenatal screening.
- Those who were not able to undergo conventional prenatal screening before 14 weeks gestation. In this case, it is still important to have a second trimester fetal ultrasound.
Verifi by Illumina (next generation sequencing): the NIPT of choice at Fertilys
1. The test is simple, accurate, and safe:
- Requires only a maternal blood test (7-10ml)
- Can be done after 10 weeks gestation (8 weeks after conception)
- Detects trisomy 21, 18, and 13
- Can detect, on request, certain sex chromosome anomalies and microdeletions
2. Offers exceptional performance:
- Detection rate (sensitivity) of 99.9% for trisomy 21, 98.3% for trisomy 18, and 98.2% for trisomy 13
- Specificity rate of 99.9% for trisomy 21, 99.9% for trisomy 18, and 99.95% for trisomy 13
3. Offers a very low rate of failure to obtain a result:
- 0,1% (compared to other types of NIPT, which demonstrate a failure rate of 5-6%)
4. Can be used even in twin pregnancies.
5. Offers a short period of delay to issue results:
- 3-5 business days
What are the advantages and disadvantages of NIPT?
As opposed to diagnostic tests such as amniocentesis or chorionic villus sampling, NIPT does not present a risk to your fetus. A simple blood test is needed. A tube of 7-10mL of maternal blood is collected, and the results are generally available quickly, within 5 business days. NIPT can be done early in pregnancy –as early as 10 weeks gestation. It is still recommended that NIPT be done after the conventional first trimester screening test, as the conventional screening result may affect the decision to undergo NIPT.
Although NIPT is superior to conventional prenatal screening, at least for the detection of trisomy 21, there are some disadvantages.
NIPT (unlike conventional prenatal screening) does not allow for the detection of the following conditions:
- Genetic syndromes or aneuploidies other than trisomy 21, 18, and 13;
- Structural fetal malformations such as cardiac anomalies;
- Adverse pregnancy outcomes such as preeclampsia, intrauterine growth restriction, and preterm labour.
NIPT is still considered a screening test rather than a diagnostic test. If the NIPT indicates an increased risk of aneuploidy, an invasive test such as amniocentesis or chorionic villus sampling is still generally required for a final diagnosis.
Even when the NIPT result indicates a low risk of aneuploidy, a fetal chromosomal anomaly can never be completely excluded.
NIPT is presently more costly than conventional prenatal screening.
A first trimester fetal ultrasound is still essential for several reasons: to accurately determine the gestational age, confirm viability of the fetus, diagnose multiple pregnancy, evaluate the fetal anatomy, and if possible examine markers of fetal well-being such as nuchal translucency, the nasal bone, intracranial translucency, blood flow in the ductus venosus and cardiac tricuspid valve, etc.
Our algorithm for prenatal screening below may help guide you in your decision-making.
For a medical consultation about Fetal DNA Test or a prenatal screening, contact FERTILYS now