Biochemical screening for Down syndrome

Maternal serum screening for Down syndrom is an established practise in man y countries. In the second trimester human chorionic gonadotrophin (hCG) or free beta-hCG is the marker of first choice, with alpha-fetoprotein(AFP) a s the second marker and unconjugated oestriol (uE(3)) the third. Statistica l models with parameters derived by meta-analysis predict that a three mark er combination will yield a 67% detection rate for a 5% false-positive rate . The model prediction have been confirmed in 21 large prospective interven tion studies. A fourth marker, inhibin A, increases the detection rate by 7 % for the same false-positive rate. In the first trimester, similar models predict that a combination of pregnancy associated plasma protein A, free b eta-hCG, AFP and uE(3) will yield a 70% detection rate. This is increased t o 88% if ultrasound nuchal translucency is used as an additional marker. Sc reening can also be extended to Edwards' syndrome, yielding high detection rates with little increase in the false-positive rate. Abnormal marker leve ls are also associated with a variety of adverse outcomes of pregnancy. Hig h quality information and decision aids are needed to minimise anxiety amon g screenees. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.