AFP and trisomy 21: The serum profiles observed in the case of fetal trisomy 21 are characterized at the end of the first trimester by decreased PAPP-A and increased free hCGβ levels; in the second trimester, it is characterized by a decrease in the AFP and uE3 levels and an increase in the hCG, free hCGβ and inhA levels [15,172] (Figure 6).