ABSTRACT
Advanced maternal age was the be all and end all of prenatal risk assessment for aneuploidy for nearly half a century. In virtually all countries, women a given age cutoff were regarded as being at high enough risk of aneuploidy to warrant the costs, hazards of performing an invasive, diagnostic procedure. Since alpha-fetoprotein (AFP) was already widely being used to screen for neural tube defects, at 16 to 18 weeks of gestation, it was relatively simple to include aneuploidy. Maternal serum AFP screening for aneuploidy was widely adopted, had the potential to increase the detection rate, but it was inefficient. While the diagnosis of Mendelian disorders may be possible by fetal cells or cell-free DNA, it is very likely that aneuploidy detection will be seen as a screening test to modify risk as a predicate for invasive diagnostic procedures. Considerable work in the mid-1990s focused on the development of ultrasound markers to be used to modify the risk of aneuploidy.
