How is Down syndrome detected?
Chueh: There are two ways: screening tests and diagnostic tests. Diagnostic tests, such as amniocentesis (usually done between 16 and 20 weeks gestation) and chorionic villus sampling (which can be done as early as 10 weeks), have the advantage of giving an unequivocal yes or no answer. However, they carry a small risk of miscarriage (1 in 200-300). In contrast, screening tests, such as the second-trimester triple screen (a blood test), present no risk to the fetus, but they can only tell a patient her relative likelihood of carrying a fetus with Down syndrome. 2. Why are experts now recommending that all women be screened? Chueh: In the past, we screened for Down syndrome based on maternal age alone. Once a woman reaches the age of 35, the risk of having a child with the condition is slightly higher than the risk of miscarriage from the diagnostic procedures, and an amniocentesis was recommended. Now better screens allow us to calculate a woman’s individual risk based not just on her
