Down's syndrome: current screening techniques.

Antenatal screening for Down's syndrome traditionally relied upon performing amniocentesis for karyotype on pregnant women aged 35 years and older. This method detects approximately 20% of all Down's syndrome pregnancies, with a false-positive rate of 4.3%. By incorporating maternal serum alpha-fetoprotein values as an additional screening parameter to maternal age, 28% of all Down's syndrome pregnancies may be diagnosed, with a 35% reduction in false-positive results. Other screening parameters such as maternal serum unconjugated estriol and human chorionic gonadotropin may eventually make it possible to detect more than 65% of pregnancies with chromosomally abnormal fetuses, without compromise in false-positive rates.