Test for trisomy 21 | Prenatal test

Test for trisomy 21

For a few years now, a blood test has been the standard procedure for detecting trisomy 21 and thus Down’s syndrome in unborn children. It is a non-invasive method, by simply taking a blood sample from the mother. Previously, it was only possible to detect trisomy by amniocentesis or chorionic villus sampling.

However, both methods carry a low risk of an unintentional termination of pregnancy. The prenatal test itself still has to be paid for. The costs are usually around 500€ and currently not covered by health insurance.

The test can be carried out from the 11th week of pregnancy, but the result is even more reliable at a later date. After sending it to the laboratory, it usually takes about 2 weeks until results are available. As pregnancy progresses, the maternal blood contains more and more parts of fetal DNA, the genetic material in which chromosomal defects can be detected.

If the result is positive for the trisomy, one of the invasive procedures must still be carried out to check the results. A suspicion of the presence of trisomy 21 can arise from a previous ultrasound examination. Individual signs in early childhood development can already provide indications of chromosomal defects. In foetuses with Down syndrome, increased neck thickness, altered nasal cartilage or heart defects discovered at an early stage may be signs. However, a diagnosis cannot be made using ultrasound.

What prenatal tests are available?

Currently pregnant women can choose between three prenatal tests:The Panorama test is one of three tests offered for the determination of trisomies (irregularities in the number of chromosomes) via the maternal blood. Here the blood is taken after the 11th week of pregnancy. The panorama test has the advantage that, in addition to trisomy 21, other chromosomal defects are also examined.

Thus, trisomy 18 and trisomy 13 are also detected with the panorama test. Both trisomies represent much more serious clinical pictures than trisomy 21. The survival rate for trisomy 18 is 6 days on average, for trisomy 13 less than one year.

However, both chromosomal defects are significantly less common than Down’s syndrome. The manufacturer of the panoramic test states that it is 99% accurate in determining the risk of trisomies. The panoramic test itself costs only 399€, but with an accompanying examination it costs around 550€.

This prenatal test cannot be performed in twin pregnancies.The DNA parts of the child in the mother’s blood are assessed, but in multiple pregnancies it is difficult to distinguish between them. The costs are only covered by the health insurance company if there is a medically significant risk, for example in the case of pregnancies of over 35-year-olds. The Harmony test is a particularly intensively scientifically investigated test.

According to recent studies, the Harmony Test detects about 99.5% of all trisomy 21 diseases. On request, other diseases can also be detected in addition to screening for trisomy 21. In addition to trisomy 18 and 13, these include the fetal sex and X or Y chromosome specific disorders, such as Turner syndrome or Klinefelter syndrome.

The costs for the test for trisomy 21 amount to 399€. However, even the Harmony test is not a reliable diagnostic tool. If the results of the prenatal test are positive, a biopsy of the placenta must always be performed to confirm the diagnosis.

The prenatal test also has the possibility to detect other chromosomal defects besides trisomy 13, 18 and 21. The manufacturer advertises with a certainty of 99.8% in screening for trisomy 21, but rare errors can never be completely excluded. The result of the Praena test is available after 4-6 days, which is an advantage over the other test procedures.

The costs for the prenatal test are given by the manufacturer as 350€ to 500€ depending on the extent of the examination. The prenatal test must normally also be paid for by the patient, but in many cases the health insurance companies already reimburse the costs. This is especially true for high-risk pregnancies and where there is a suspicion due to prior examinations.