Prenatal Genetic Screening

Excerpt

The first prenatal screening test was introduced in the 1970s: a single second-trimester serum test for maternal serum alpha-fetoprotein, a marker of neural tube defects. Aneuploidy screening using maternal serum markers was introduced in the 1980s, and the number and complexity of offered screening tests have been on an upward trajectory ever since. Prenatal genetic screening is used to assess whether there is an increased risk of the fetus being affected by a genetic disorder. Originally, prenatal genetic testing primarily focused on trisomy 21 (Down syndrome), but now it can detect a broad range of genetic disorders. Today, prenatal genetic screening falls into four categories: ultrasonography, maternal carrier status of specific genetic disorders, maternal serum assays looking for specific biochemical markers indicative of aneuploidy, and most recently, maternal plasma fetal cell-free fetal DNA (cffDNA), which has been used for aneuploidy, microdeletion, and copy number variants (CNVs). Maternal serum assays include first-trimester screening, the triple screen, the quadruple screen, and the penta screen. There is also the option of combining first-trimester and second-trimester screening with either integrated, sequential, or contingent screening protocol. This provides a higher detection rate than a one-step screening.