Hello Chidy,
Are you talking about the OSCAR test at Prince of Wales Hospital? I talked to my doctor (private clinic) that this is a paid-for -service of the CUHK which comprises a neck thickness measurement and blood test at 14 weeks (first trimester). He told me most of the centres, like HKU, are still using second trimester blood test for the time being. CUHK is only trying to develop first trimester screening as research at the current status.
My doctor has already performed neck thickness measurement for my baby & I will receive blood tests for Down's Screening in 17th week.
So i think it doesn't matter if you choose to do this OSCAR test in 1st trimester or do it in 2 times in 2 visits at your doctor.
Hope this helps!
Peggy