Protocol 5 - In this protocol, Norton reviews the pathophysiology of fetal aneuploidy and the wide range of tests for it. Included are perspectives on cell-free DNA testing, first-trimester combined screening, nuchal translucency (NT) sonography, and pregnancy-associated plasma protein A (PAPP-A) and human chorionic gonadotropin (hCG), as well as quad marker screening in the second trimester in appropriate cases, and combined first- and second-trimester screening.
Trisomies 21, 18, and 13 are the most common autosomal trisomies. Triploidy and deletions and duplications of portions of chromosomes also occur. With the advent of chromosomal microarray analysis, it is now possible to identify submicroscopic abnormalities associated with significant genetic diseases.