MARKERS OF FETAL TRISOMY-21 IN MATERNAL S ERUM

Down's syndrome is the most frequent genetic disease. Each year, in Fr ance, there are 1 100 trisomy 21-affected newborns. This chromosomal d isease is the most frequent cause of mental retardation raising an imp ortant public health problem. Prenatal diagnosis of chromosomal anomal ies is based on fetal karyotyping, but cannot be proposed in all situa tions because of the cost and the risk of fetal death due to amniocent esis. The aim of screening is to define patients at increased risk for trisomy 21. Three criteria are currently used to define an at risk-po pulation: maternal age, ultrasound anomalies, and maternal serum marke rs. In France, amniocentesis is proposed to patients over 38 years of age. Ultrasound signs for trisomy 21 are often difficult to identify a t routine echography. Based on a prospective study of 51,048 women und er 38 years of age, we observed that maternal serum hCG at 15 weeks ca n detect 59% of all trisomy 21 cases while the yield for amniocentesis is 6.1%.