Yael - Yum Cha is kind of like chinese antipasto! They bring around chinese small foods - dumplings, spring rolls, chinese broccoli in Oyster etc things that you would find on a chinese appetiser list. The wait staff bring it around of trolley's and you simply take what dishes you like and they stamp a little cardboard ticket which they tally at the end!
Its yummy.
Noe to answer the questions, Cha is fine when preggo. Just keep in minf the stuff you should avoid and you should be fine. I ate heaps when I was pregnant and was fine. After all Chinese women have babies (and lots of them!) and they must eat it too!