Maternal serum markers. Estimation of the risk of Down's syndrome: a prospective study.

The risk of Down's syndrome pregnancies can be estimated by quantitation of maternal serum markers, namely alpha-fetoprotein, unconjugated estriol and human chorionic gonadotropin (triple test). A prospective study of 2892 pregnant women (median age 33.5 years) is reported. The detection rate of Down's syndrome pregnancies was 80% (confidence intervals 45%-100%) when a risk of 1:380 or greater was considered "screen positive", the false positive rate was 13.3% (confidence intervals 12.0%-14.5%). The importance of the accurate assessment of gestational age and the time of blood sampling are emphasized. Our findings are compared with similar studies performed in other laboratories.