Baby growth and GD test (kkh)

Hi I just went for my week 20 detailed scan at kkh as subsidize patient. After the scan I ask the doc on baby length and weight but doc say for now they don't measure it based on weight or length. I will be going for my GD test next month, maybe I know will we be able to see baby and know his length and weight during then or just purely blood test? Can some one advice please? Thank you.