About TRISOMY test
TRISOMY test is a non-invasive maternal blood test which can – thanks to its high sensitivity and specificity – exclude the presence of chromosomal abnormalities as early as in the 11th week of pregnancy. If the mother-to-be wishes to know, the test can also determine the sex of her unborn baby.
Compared to other screening methods, TRISOMY test:
- has a higher sensitivity and specificity with regard to the disorders monitored,
- minimizes false positive results,
- reduces the number of necessary amniocenteses,
- poses no risk to either the mother or the child.
If the mother-to-be wishes to know, TRISOMY test can also determine the sex of her unborn baby.
Fetal DNA is already present in maternal blood in early stages of pregnancy. Thanks to a special screening laboratory procedure, it is possible to isolate and analyse foetal DNA to determine the risk of trisomy (three identical chromosomes).
thanks to high sensitivity
without any sampling risks
using only maternal blood
results available within 5 days
as early as in the 11th week of pregnancy
The test can exclude
frequent chromosome number disorders (chromosomes 21, 18 and 13) called trisomy *
It can detect
potential false positive results of biochemical prenatal screening tests.
the necessity of amniocentesis (invasive sampling of amniotic fluid).
It can determine
the sex of your unborn child, if you are interested to know.
* the cause of Down, Edwards and Patau syndromes
Down syndrome detection rate
1 The percentage indicates the number of positive results detected by the screening test at a false positive rate of 4.5 %.
2 The percentage refers to no other foetus defect than Down syndrome.
3 In an extended validation study, TRISOMY test showed a sensitivity of 100% (95% Confidence Interval 83.89–100%) and a specificity of 99.95% (95% Confidence Interval 99.70–100%)
4 Compared to standard TRISOMY test screening, the detection sensitivity of TRISOMY test + is comparable, possibly even higher.
* In compliance with a resolution adopted by the Ethics Committee of the Slovak Ministry of Health, our laboratory only provides test results to patients once they have completed their 12th week of pregnancy. The test result is disclosed and interpreted to the patient by the doctor who referred the patient for the test.
Read more about the sensitivity of non-invasive prenatal testing (NIPT)
Offered by various laboratories, non-invasive prenatal tests (NIPTs) detect specific chromosome 21, 18 and 13 and sex chromosome number abnormalities. The tests yield results that do not reveal any information on genetic or morphological foetal or maternal disorders other than those they are designed to target. Screen-positive NIPT results must be subsequently validated by analysing a sample obtained using an invasive method.
Trisomy 21 (Down syndrome)
NIPT screening can detect more than 99% of trisomy 21 cases. Generally speaking, only 1 in 1,650 trisomy 21 NIPT results based on normal pregnancies (0.06%)* has been identified as false positive. As for TRISOMY test, only 1 in 1,842 results based on normal pregnancies has been identified as false positive (i.e. less than 0.05%). The results of our latest validation study involving a set of samples obtained from pregnant women and a set of samples containing fetal trisomy 21 showed that our TRISOMY test is highly sensitive.
Trisomy 18 (Edwards syndrome)
The sensitivity of NIPTs for trisomy 18 is lower than their sensitivity for trisomy 21, namely 90%*. The false positive ratio is 0.01%*. TRISOMY test false negative result ratio (1 in 9 cases*) is comparable to the global ratio (1 in 10 cases*).
Trisomy 13 (Patau syndrome)
Prospective studies rarely include trisomy 13 cases, which makes NIPT sensitivity and specificity calculations for this type of syndrome rather difficult. In a recent international study based on 11,185 samples, 2 out of 2 positive cases were successfully identified*. The false positive ratio for this type of trisomy in this particular study reached 0.02%*. As for TRISOMY test screening, 3 out of 3 trisomy 13 cases were correctly identified, the false positive ratio being 0.05%.
* – DOI: 10.1056/nejmoa1407349#t=article
Sex chromosome syndrome
In international studies, syndromes associated with abnormal numbers of sex chromosomes, whose incidence rate is either 1 in 490 (Klinefelter syndrome, XXX syndrome, and XYY syndrome) or 1 in 2,700 (Turner syndrome), show detection ratios of 93% and 90%, respectively. The false positive ratios for the two groups of syndromes reach 0.14% and 0.23%, respectively, the accuracy of the method being higher than 99%** in both cases.
Prospective studies rarely include microdeletion syndrome cases, which makes NIPT sensitivity and specificity calculations rather difficult. However, available data suggest that the detection rate for microdeletion aberrations reaches 83% for deletion scopes larger than 6 million bases and 20% for deletion scopes of up to 6 million bases on condition that standard genomic sequencing is applied (4-10 million readings per sample)***.
* – DOI: 10.1056/nejmoa1407349#t=article
** DOI: 10.1002/uog.14791; DOI: 10.1186/1750-1172-1-42
*** DOI: 10.1016/j.ajhg.2015.11.016
TRISOMY test and TRISOMY test + results
Non-invasive prenatal test results provide information about a selected number of the most frequently occurring genetic chromosomal disorders (up to 85 % of all foetal genetic disorders). It must be borne in mind that they cannot identify all existing genetic or developmental disorders.
If negative, NIPT test results can help you avoid invasive diagnostic testing, such as amniocentesis, which carries certain risks associated with amniotic fluid sampling.
Please note: Despite its high sensitivity and specificity in detecting fetal chromosome 21, 18 and 13 trisomy, TRISOMY test is considered a type of screening, not a diagnostic method. Consequently, a positive result must always be confirmed by amniocentesis or chorionic villi sampling.
A negative TRISOMY test result need not be confirmed by diagnostic amniocentesis, which means, in most cases, that the mother-to-be can avoid invasive tests and the risks they come with.
In the event that your TRISOMY test result is positive, you should arrange an appointment with a specialist in genetics, who will refer you for examinations required in the circumstances.
In a small percentage of cases, the method does not lead to unequivocal results and the laboratory analysis is concluded to be unsuccessful. In the circumstances, such results are labelled “non-informative”, i.e. of no diagnostic value. Chromosome analysis may be unsuccessful because of a low fetal DNA concentration in maternal blood. However, a low fetal DNA concentration in maternal blood is not to be understood as a reason for concerns as it occurs naturally in about 5% of all pregnant women. The concentration of fetal DNA gets progressively higher further on in pregnancy.
*If a blood sample cannot be processed by the laboratory in accordance with the principles of good laboratory practice, or if the analytical results do not provide an answer to the diagnostic question, the laboratory offers a repeat examination based on the same blood sample free of charge (in the circumstances, the period for the delivery of test results will change from 5 to 8 days).
If a repeat examination based on the same blood sample yields a non-informative result, the mother-to-be will be advised to repeat the test 14 days later, which is free of charge and almost always leads to unequivocal test results.
Patients’ and Doctors’ Views
I have always wanted to be a mother, but I only managed to get pregnant when I was 37 thanks to IVF. Since this was going to be my first and probably the only child, I made absolutely sure everything was going to be perfect. I found amniocentesis risky, and when I found out about TRISOMY test, I did not hesitate. It is so simple and painless - and the reassurance is priceless.