Pinkimum,
The OSCAR/NT scans are usually performed from 11 to 13 weeks + 6 days of pregnancy. Before 11 weeks the scan is technically difficult because the baby is so tiny and, after 14 weeks, excess NT fluid may be absorbed by the baby's developing lymphatic system.
Supplements: Once my family learnt about my pregnancy, my mum starts piling me with supplements, calcium lah, Phoschol (i have no idea wat this is) and so on. Brought everything to my gynae, and he told me to stop everything except folic acid and the pre-natal vitamin (obimin). Hahahahha... my mum so disappointed. I think better to let the gynae see and decide for you loh.