Sorry - I should have updated this thread. Apparently the placenta was never in the way. I wasn't able to get a scan or see my OB when I got home because of Christmas and everyone's holidays away. I finally got my scan at the end of December and asked the sonographer how it was looking. She was so confused by what the OB in HK had said that she went to get the specialist practitoner to come and check my scan too because she didn't see how it could possibly have been classed as low lying, let alone placenta praevia, only three or so weeks earlier. My OB said the same thing when I saw him later the same day.

It was still very worrying for us for a while because I lost a lot of blood with pretty sizeable clots, but touch wood haven't had any bleeding since so the worry has eased. I'm getting scans regularly to keep an eye on bub and so far so good. Given it was so far after the fact my Ob saw me and he couldn't see anything on scans, he couldn't suggest a cause other than I had been doing too much physically, carrying the girls around too much etc. I had bleeding on and off (although never to this extent) with both DDs so maybe its just something I do?