@tuna As someone has shared, OSCAR is done around 12weeks. It comprises of a blood test and a scan. Both results are combined to give a final OSCAR result that comes in a ratio number. In nutshell, it tests for Down syndrome PROBABILITY.
I stress the word probability because that's something I don't like about OSCAR. To me, it can be ambiguous to a certain extend (Google and you can find so many couples posting their OSCAR results in forums to ask if their numbers are healthy, risk-free, etc). I find the result format leaves many couples worried unnecessarily.
Any MTBS can opt for OSCAR but I find its best suited for those who are in the low risk group (aka younger, etc) because OSCAR takes into your age number to calculate its risk.
Since me lao charbor, I prefer Harmony test that reflects result in a more "humane" way. Ha. Result will come out as an absolute Low or High risk and to me that's a clearer answer, rather than a ratio which leaves too much for imagination.