Similarly, hCG, unconjugated estriol (uE3), alpha-fetoprotein (AFP) and dimeric inhibin-A (DIA) are measured in the four-analyte screen used in the second trimester for the detection of trisomy 18 (71%–100% detection rate at a 0.3% false-positive rate) and trisomy 21 (67%–71% detection rate at a 5% false-positive rate) [24,32]. This evidence concerns the gene AFP and trisomy 18.