A new test, which consists in making a blood test to the pregnant woman to examine the DNA of the developing fetus that contains the blood of the mother, is capable of detecting Down's syndrome and other chromosomal anomalies -such as trisomy 18-, so it would no longer be necessary to use invasive tests, such as amniocentesis, to diagnose this disorder.

In addition to ultrasound and blood tests to determine the presence of certain substances in the mother's blood that may indicate a problem, there are two other tests that are used to screen for malformations during pregnancy when the risk is considered high. , corial biopsy and amniocentesis, which are invasive and present a certain risk of miscarriage, which is greater in the case of biopsy.

This new prenatal diagnostic test - which can be performed after week 10 of pregnancy - would prevent these invasive tests, and will be available in Spain, in around 50 private hospitals, from January, at a price of around 700 euros. . The analysis would be indicated in those cases in which the first screening - the ultrasound, the analyzes and the age of the mother - implied a significant risk that the fetus would present alterations.

It must be borne in mind that the first screening with non-invasive tests only detects 85% of the cases in which malformations exist, with 5% false positives. These false positives, moreover, would be easily ruled out with the new blood test, without the need to resort to amniocentesis.

The previous tests that have been carried out with the new test give it a reliability of 99% and a false positive rate of only 0.1% in the cases of the most frequent trisomies, 21, which causes Down syndrome, and 18, responsible for the Edwards syndrome. It is also able to identify trisomy 13-Patau- syndrome, although the effectiveness is somewhat lower for this disorder, and it is reduced to approximately 89%.

At the moment, the specialists do not advise the test when the pregnancy has been achieved through a donation of oocytes, or in multiple pregnancies, because its effectiveness has not yet been confirmed in these cases.

Amnio vs. Genetic Blood Testing (November 2019).