Dépistage de la trisomie 21 par les marqueurs sériques

Prenatal diagnosis of aneuploidies is based on foetal karyotyping. Prenatal screening consists in targeting patients with an increased risk of chromosomal abnormality for whom amniocentesis will be proposed. Maternal marker screening for Down syndrome is based on an individual risk calculation obtained by weighting the risk due to maternal age by a factor linked to maternal serum markers. Four markers are currently used during the second pregnancy trimester: AFP, hCG or free β-hCG, and oestriol. In France, this screening has been organised since 1997 and is subject to strict regulation. The results of the 72 accredited laboratories are known at a nationwide level: screening is performed in 80% of pregnant women, 70% of trisomy 21 cases are detected for a 6.5% amniocentesis rate. Because maternal serum screening usually follows first-trimester nuchal translucency measurement, it would be interesting to combine the two methods instead of performing them sequentially. First-trimester maternal serum markers (free β-hCG and PAPP-A) are not currently used in France. The future consists of the use of combined tests, first- or second-trimester serum markers and nuchal translucency measurement.