When is the best time to do the Down syndrome screening?

Patient's question:

Main symptoms: History of Down syndrome
Onset time: Born in 2004
Laboratory test results:

Doctor's answer:

Hello, the Down syndrome screening is a test performed between weeks 15 and 21 of pregnancy. It is recommended by your doctor based on your health condition, and it can only be used as a reference. It is advised to undergo regular prenatal check-ups and follow the advice of your obstetrician. Wishing you good health!