The first trimester screening is a combination of test for PAPP-A, HCG and nuchal translucency which are usually used to assess the risk which the fetus a pregnant woman is carrying has a chromosome disorder such as Down syndrome (trisomy 21) or Edwards syndrome (trisomy 18). The patients may be first offered for the first trimester screen for prenatal Down syndrome screening and other options offered includes the second trimester maternal serum screen and the cell-free fetal DNA test.