Advances in antenatal screening for Down Syndrome

Antenatal screening for Down Syndrome using maternal age alone is no longer an adequate standard of care. Screening in the early second trimester of pregnancy (between 15 and 20 weeks of pregnancy) using the quadruple test can identify 76% of affected pregnancies with a 5% false-positive rate. Screening in the first trimester of pregnancy (between 10 and 13 weeks of pregnancy) is possible using two biochemical markers (PAPP-A and free β-hCG) together with an ultrasound marker nuchal translucency measurement; using these three markers together with maternal age can identify 85% of affected pregnancies, with a 5% false-positive rate. While there is debate over issues involved in choosing between first and second trimester screening, the most effective screening test for Down Syndrome is the integrated test based on the integration of the first trimester and the second trimester markers. This has a 94% detection rate for a 5% false-positive rate. If the false-positive rate were set at 1%, the detection rate would be 85%. No other screening test for Down Syndrome can detect such a high proportion of affected pregnancies with such a low false-positive rate.