How many weeks of pregnancy can you do the Down syndrome screening?

Patient's question:

Thank you for the doctor's quick answer for me - how to treat and prevent

Doctor's answer:

A Down syndrome screening is a method that involves drawing a pregnant woman's blood to test the concentration of alpha-fetoprotein and human chorionic gonadotropin in the maternal serum, and then calculating the risk coefficient of giving birth to a child with Down syndrome by combining the pregnant woman's estimated due date, age, weight, and gestational age at the time of blood collection. The optimal time for screening is between the 15th and 20th weeks of pregnancy.