Question
What is the definition of Down syndrome, and what risks do individuals with Down syndrome face?
Answer
Down syndrome, also known as trisomy 21, refers to a condition where an individual has an extra copy of chromosome 21. The risk of Down syndrome is assessed through measuring levels of alpha-fetoprotein (AFP) and human chorionic gonadotropin (HCG) in the pregnant woman’s blood, combined with her age, weight, and gestational age. Generally, a risk value over 1/275 is considered high risk, while below this value is considered low risk. The incidence of Down syndrome in the general population (under 37 years of age) is approximately 1 in 750. Prenatal screening for Down syndrome aims to evaluate the risk of the fetus having Down syndrome through blood tests. If the risk is high, further diagnostic tests, such as amniocentesis or chorionic villus sampling, are recommended. It is important to note that screening results only provide a risk estimate and not an absolute judgment, thus reducing unnecessary psychological burden.