Screening test is what is offered to the population (pregnant women) as a first line and can only differentiate between a high risk and low risk. Screening test cannot say fetus is “normal” or has “Down syndrome” but can only give the risk of the fetus for Down syndrome. Diagnostic test is what can diagnose or rule out Down syndrome. It is an invasive test (amniocentesis or chorionic villus sampling) which can diagnose by looking at the karyotype. It is only offered in case of high-risk results and not first line. Biochemical screening using biochemical tests for purposes of detecting the presence of a disease. Combined first trimester screening, quadruple screening test, triple screening test, and noninvasive prenatal test are covered in this chapter.