Effectiveness of crosstrimester test in selecting high-risk pregnant women to undergo invasive prenatal diagnosis

The effectiveness of serologic and echographic non-invasive prenatal screening (IPS) in identifying pregnant women at increased risk for aneuploidies independently from maternal age alone has been consistently documented (Kazerouni et al., 2009; Muller et al., 2002). Non-IPS tests are applied in the first and second trimester of pregnancy, alone or in association with ultrasound scan, allowing the detection of 80-90% or more of Down syndrome (DS) cases (ACOG, 2007; Benn et al., 2007; Malone et al., 2005; Nicolaides, 2003). In this context we report the results of a non-IPS test (“crosstrimester test”), which incorporates the ultrasound and serologic risk estimates of first trimester screening tests with the serologic risk estimates of second trimester screen. Compared with the fully integrated test (Malone et al., 2005), we added free-beta-hCG to the serologic tests of the first trimester, and used triple test in the second trimester.