Screening for Down's syndrome in the first trimester of pregnancy

Down's syndrome accounts for roughly one third of all causes of mental handicap. It has a prevalence of 0.2% of all pregnancies and, with the availability of prenatal diagnosis by chorionic villus sampling or amniocentesis, every obstetrician faces the challenge of counseling his patients about chromosomal abnormalities. Combining quantifiable fetal markers with the maternal age-related risk individualises the risk calculation and improves the detection rate of Down's syndrome. Thus, at a 5% false-positive rate, the detection rate is 30% for age-based screening (age cut-off of 37 years in Germany/Austria), and if the nuchal translucency measurement and maternal serum concentrations of free b-human chorionic gonadotrophin (hCG) and pregnancy associated plasma protein A (PAPP-A) are taken into account, the detection rate increases to about 90%. This information should be provided to every pregnant woman.