How far along in a pregnancy can you tell if its twins?

Answer 1

I had a scan at 8 weeks and was told I was having twins and saw there were two foetuses (prior to this I had dreamt it was twins).

Also when I took the pregnancy test, just as my period was due, the line on the test was really really dark. Once I discovered I was having twins I realised the line had been really dark because of my elevated levels of HGC. A faint line would have been expected so early in the pregnancy, when HGC is rising, but HGC rises faster in twin pregnancies than singleton ones, so the early indication of a high level of HGC was an early sign it was twins.