Final answer:
The quad screen is a blood test used during pregnancy to evaluate the risk for chromosomal abnormalities such as Trisomy 18 and Trisomy 21, with the risk for these conditions increasing with maternal age.
Step-by-step explanation:
The quad screen is a prenatal test that measures levels of four substances in a pregnant person's blood: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), estriol, and inhibin A. It is used as part of the screening process for certain chromosomal conditions, including Trisomy 18 and Trisomy 21 (Down syndrome). High levels of AFP in a child previously treated for teratoma may suggest a relapse with an endodermal sinus tumor, emphasizing the importance of monitoring cancer survivors after treatment.
Trisomy, such as Trisomy 18, occurs when there are three copies of a chromosome instead of the usual two. This results in 47 chromosomes in total. A procedure called karyotyping can show the number of chromosomes present and reveal any abnormalities. The incidence of trisomy conditions like Trisomy 21 (Down syndrome) increases dramatically with the age of the pregnant person, which is also important information for the counseling and management of pregnancy.