First-trimester biochemical screening for Down syndrome

Of all markers evaluated for first-trimester biochemical screening for Down syndrome (DS), PAPP-A and free beta -hCG emerged as the most predictive. The combined test uses these markers in AV conjunction with nuchal translucency measurements, and is estimated to achieve a DS detection rate of 80% to 85% at a 5% false-positive rate. The integrated test, combining first-trimester sonographic and biochemical markers with second-trimester markers, provides a single estimate of a patients DS risk, and may yield a DS detection rate of 94% at a 5% false-positive rate. The acceptability and feasibility of this test, however, remain to be proved.