Screening for Down syndrome.

Screening for Down Syndrome was initially only related to maternal age and has successively developed by introducing biochemical markers and algorithms to estimate the risk for particularly trisomy 21 and 18. We now have a long experience of screening with four biochemical markers, alpha-fetoprotein, total hCG, unconjugated estriol and free β-hCG during the second trimester. Screening is now moving towards screening in the first trimester using a combination of ultrasound (Nuchal Translucency) and the maternal serum biochemical markers free β-hCG and Pregnancy Associated Plasma Protein-A (PAPP-A). This has become known as the combined test. Several maternal and pregnancy factors which can influence the concentrations of biochemical markers are discussed. The possibilities of screening for other aneuploidies in the first trimester and an outline of recent methods to improve overall screening performance are highlighted and the review will suggest some possible options for the future in which Cell Free DNA techniques may become part of an improved overall screening strategy. In conclusion it is emphasized that the time has come to invert the Pyramid of Antenatal Care to focus on the 11-13 week assessment.