Down syndrome test: blood test for early detection
Since 2012, a non-invasive method of prenatal diagnosis has made it possible to detect Down syndrome by taking a simple blood sample. Unlike first-trimester screening, the results of the test are 98 percent certain. Find out more about the blood test here and learn more about the procedure, reliability and costs of the procedure.
Trisomy 21 – also known asDown syndrome– refers to a chromosomal abnormality in which chromosome 21 is present three times instead of only twice, resulting in physical and mental impairment of the affected children. One in about 600 children in Germany is born with Down syndrome, although statistically the numbers are higher with increasing age of the mother.
Even during pregnancy, mothers can detect genetic peculiarities in their child. Thefirst trimester screeningworks without a direct intervention in the mother’s body, but only probabilities can be made on the basis of the results, but no reliable statements. For a reliable diagnosis, a cell sample with the DNA of the child is necessary, which previously only invasive methods, such asamniocentesis, could provide. Even though these procedures are now standard in prenatal diagnosis, they are not harmless and can trigger various complications, in rare cases even a miscarriage. With the help of the blood test, the health of mother and child is better protected and at the same time safe results are provided.
How does the non-invasive Down syndrome test work?
In the mid-90s, it was proven that parts of the child’s genetic material swim in the mother’s blood. These DNA sequences of the fetus are stuck in dead cells that enter the mother’s bloodstream via the placenta. Through a procedure officially introduced in 2012, the so-called “Next Generation Sequencing”, it has been possible to isolate these sequences from a simple blood sample from the mother and assign them to the various chromosomes. If more sequences are found for chromosome 21 than are actually intended, doctors can diagnose Down syndrome with a high degree of certainty or, conversely, rule it out if fewer sequences are found.
How does the blood test differ from other methods of diagnosing Down syndrome?
The most important point is certainly that a reliable diagnosis can be made in the blood test without endangering the health of the mother or her unborn child by a puncture. As with the invasive procedures, the blood test checks sequences for other chromosomes, for example 18 and 13, in addition to the sequences for chromosome 21. However, recognition rates for other chromosomes are lower than for chromosome 21. In contrast to examinations such as the amniocentesis, the blood test can be used as early as thetenth week of pregnancy.
In what cases is the blood test performed?
The blood test is not intended to replace the first trimester screening, but is recommended on the basis of a critical finding, in risk groups or corresponding medical history in the family. It is therefore not intended as a routine examination, also due to the high costs, despite the uncomplicated procedure.
The cost of a blood test is between 130 and 540 euros, consultation and blood collection cost an additional 50 to 60 euros, as familienplanung.de informed. What exactly results in the price for the blood test depends on the scope and provider. Your gynecologist will give you the necessary information.
Does the health insurance cover the costs of the blood test?
In the past, health insurance companies did not cover the costs of the blood test for chromosomal abnormalities. In mid-2019, however, the Federal Joint Committee (G-BA) of health insurance companies, doctors, clinics and patient representatives decided in principle that the non-invasive prenatal test (NIPT) will be covered by health insurance – however, this service is not expected to come into force until June 2021. The most important argument for the future health insurance benefit: The blood test is risk-free compared to older analysis methods for mother and child.
How reliable are the results?
Various extensive practical studies have shown that this method is more than 99 percent correct and thus delivers similarly good results as amniocentesis orchorionic villus sampling.
Nevertheless, the blood test does not guarantee 100% safety. Parents should keep this in mind in any case. As familienplanung.de explains, the test provides a risk rating, not a conclusive diagnosis. The results are divided into three risk findings:
- “Low risk”: The test has shown that there is no chromosomal abnormality with a probability of over 99 percent.
- “High risk”: The status of the pregnant woman plays a significant role in this classification. If it belongs to a risk group, there is a probability (in 9 out of 10 cases) that there is a chromosomal abnormality. If it does not belong to a risk group, the test is not reliable for this classification.
- “Unclear findings”: If the findings are unclear, there may be several reasons. “For example, studies have shown that there is not always enough fetal DNA in the blood of obese women to successfully use the test,” says familienplanung.de. This result is possible in 2 to 6 out of 100 pregnant women. A new blood test can provide clarity here.
Parents who are looking for certainty no longer need to fear the risks of an examination with the blood test. What happens after that, however, remains a difficult decision. More information on this topic can be found in our article “Abortion for Down Syndrome?” or in the area of “disabled children”.