Several studies showed that 10 % of the free DNA found from the first quarter of the pregnancy in the maternal plasma is of foetal origin and that this DNA is specific of the foetal nuclear DNA of the current pregnancy. This opened the way of a possible not invasive antenatal diagnosis of the foetal aneuploidy which collided during the last 10 years with the performances limited by the isolation and by the sequencing of the foetal DNA in the maternal plasma. A new technique of analysis by broadband sequencing of the DNA circulating in the maternal blood for the diagnosis of the most frequent aneuploid the trisomy 21 of which was brought back(reported). The High-output shotgun sequencing of all the DNA circulating in the maternal blood, then the reading and the identification of all the chromosome sequences allows to analyze the quantity of DNA resulting from the supernumerary chromosome, without necessity of differentiating maternal and foetal DNA. On the basis of very recent works 10, this excess of sequences resulting specifically from the chromosome 21 foetal supernumerary allows a discrimination completes between trisomy 21 and disomy 21. However, this study analyzed only 9 cases of trisomy 21 and the sampling of maternal blood were realized after the amniocentesis or the choriocenteses, what could artificially have increased the quantity of circulating foetal DNA.