1. Trisomy 21 affects chromosome 21.

2. Trisomy 21 is a congenital defect causing mental retardation.

3. Thus, Trisomy 21 is commonly known as Down syndrome.

4. Further investigations for foetal and obstetric abnormalities other than trisomy 21, can be performed.

5. The accelerated aging suggest that trisomy 21 increases the biological age of tissues, but molecular evidence for this hypothesis is sparse.

6. AMNIOCENTESIS, ANOMALIES CONGÉNITALES, CONGENITAL ANOMALIES, DIMERIC INHIBIN-A, GROSSESSE/ACCOUCHEMENT, HEALTH SERVICES, LES SERVICES DE SANTÉ, PAPP-A, PREGNANCY/BIRTH, PRENATAL SCREENING, REPRODUCTION/GROSSESSE, REPRODUCTION/PREGNANCY, SERUM BIOCHEMISTRY MARKERS, TRISOMY 21 Abstract:

7. The best performing screening tests are able to identify more than 90 % of trisomy 21 cases with a 5 % rate of false positives but positive screening results require confirmation with diagnostic testing, such as amniocentesis or chorionic villus sampling (CVS).