Blood test for trisomy 21, 13 and 18
(NIPT, non-invasive prenatal testing)
Since 2012 a non-invasive diagnostic test has been available, which can show evidence of, or rule out, trisomy 21 in a foetus and also trisomy 13 and 18 with a high degree of reliability by taking a sample of the mother’s blood ((e.g. PraenaTest® from PraenaBayern, Harmony-Test® from Ariosa)).
The test is offered first and foremost to patients with an intermediate or increased risk of trisomy 21, 13 or 18 (e.g. after an abnormal first trimester screening or abnormal serum biochemistry) from the 12th week of pregnancy onwards if a further diagnosis is required, but a risk of intervention needs to be avoided. Details of the indication must, however, always be clarified on an individual basis during a consultation, as is also prescribed by law.
The blood test to detect trisomy 21, 13 or 18 from maternal blood is not currently to be seen as a diagnostic test, but rather as a screening test with the highest level of reliability. An abnormal test result must always be confirmed by an invasive diagnostic procedure (chorionic villus sampling, amniocentesis, placentacentesis). A normal test, on the other hand, can rule out trisomy 21, 13 or 18 with a high degree of certainty. However, an abnormal first trimester screening (particularly an enlarged nuchal fold) can also indicate other chromosomal defects or disorders, such as a heart defect (see also 1st trimester).
The test does not therefore represent a substitute (e.g. for the first trimester screening), but an additional instrument in prenatal diagnostics. The test must thus be preceded by a differentiated ultrasound examination (e.g. as part of a first trimester screening from the 12th week of pregnancy or a precise sonographic diagnosis from approx. the 16th week of pregnancy) in order to assess the morphology of the foetus with the highest possible precision.
If, after an ultrasound examination, a non-invasive clarification of trisomy 21, 13 and 18 is required and this is consistent with the required medical indications, we will discuss and plan the necessary steps for this with you.
The blood test is not suitable for detecting chromosomal defects other than trisomy 21, 13 or 18 or for detecting balanced chromosomal defects. Nor, for example, are tessellations or different chromosome patterns in the placenta and baby reliably registered. Details about these limitations are dealt with in the consultation.
Please bear in mind that the costs for the examination are not currently accepted by the health insurance schemes as a rule, but must be borne by the patient. Amounts between 300 and 400 euro are invoiced directly to the patient by the companies providing the service.
We can offer the blood test for trisomy 21, 13 or 18 through our establishment. The blood test can only be carried out, however, in connection with an individual genetic consultation and a precise ultrasound diagnosis (first trimester screening or differentiated ultrasound diagnosis). Please get in touch with us over the phone to arrange an appointment concerning this matter.