the 20weeks scan is more for the anatomy and physical aspects of the baby. u will still need to go for other tests to check if there is any genetic deficiencies such as Oscar or NIPT (which was usually done at week10)
I only did the detailed scan and drawn my blood once for Oscar that’s all. Low risk pregnancy and afraid of needles hence I didn’t go for GD/any other vaccinations 😅. Baby is full term and healthy.